Ion sources, systems and methods

ABSTRACT

Ion sources, systems and methods are disclosed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of, and claims priority under35 U.S.C. §120 to, U.S. application Ser. No. 10/966,243, filed Oct. 15,2004, which claims priority under 35 U.S.C. §119(e)(1) to U.S.Provisional Application Ser. No. 60/511,726, filed Oct. 16, 2003. Thisapplication is also a continuation-in-part of, and claims priority under35 U.S.C. §120 to, U.S. application Ser. No. 11/147,102, filed Jun. 7,2005. This application is also a continuation-in-part of, and claimspriority under 35 U.S.C. §120 to, U.S. application Ser. No. 11/146,741,filed Jun. 7, 2005. This application is also a continuation-in-part of,and claims priority under 35 U.S.C. §120 to, U.S. application Ser. No.11/385,136, filed Mar. 20, 2006. This application is also acontinuation-in-part of, and claims priority under 35 U.S.C. §120 to,U.S. application Ser. No. 11/385,215, filed Mar. 20, 2006.

This application claims priority under 35 U.S.C. §119(e)(1) to: U.S.Patent Application Ser. No. 60/741,956, filed Dec. 2, 2005; U.S. PatentApplication Ser. No. 60/784,390, filed Mar. 20, 2006; U.S. PatentApplication Ser. No. 60/784,388, filed Mar. 20, 2006; U.S. PatentApplication Ser. No. 60/784,331, filed Mar. 20, 2006; U.S. PatentApplication Ser. No. 60/784,500, filed Mar. 20, 2006; U.S. PatentApplication Ser. No. 60/795,806, filed Apr. 28, 2006; and U.S. PatentApplication Ser. No. 60/799,203, filed May 9, 2006.

Each of these applications is incorporated herein by reference.

TECHNICAL FIELD

The disclosure relates to ion sources, systems and methods.

BACKGROUND

Ions can be formed using, for example, a liquid metal ion source or agas field ion source. In some instances, ions formed by an ion sourcecan be used to determine certain properties of a sample that is exposedto the ions, or to modify the sample. In other instances, ions formed byan ion source can be used to determine certain characteristics of theion source itself.

SUMMARY

In one aspect, the invention features a system that includes a gas fieldion source capable of interacting with a gas to generate an ion beamhaving a spot size with a dimension of 10 nm or less at a surface of asample.

In another aspect, the invention features a system that includes an ionsource capable of interacting with a gas to generate an ion beam havinga spot size with a dimension of three nm or less at a surface of asample.

In a further aspect, the invention features a system that includes a gasfield ion source capable of interacting with a gas to generate an ionbeam having a brightness of 1×10⁹ A/cm²sr or more at a surface of asample.

In an additional aspect, the invention features a system that includes agas field ion source capable of interacting with a gas to generate anion beam having a reduced brightness of 5×10⁸ A/m²srV or more at asurface of a sample.

In one aspect, the invention features a system that includes a gas fieldion source capable of interacting with a gas to generate an ion beamhaving an etendue of 5×10⁻²¹ cm² sr or less.

In another aspect, the invention features a system that includes a gasfield ion source capable of interacting with a gas to generate an ionbeam having a reduced etendue of 1×10⁻¹⁶ cm²srV or less.

In a further aspect, the invention features a system that includes a gasfield ion source including an electrically conductive tip. The gas fieldion source is capable of interacting with a gas to generate an ion beamfor a time period of one week or more without removing the electricallyconductive tip from the system.

In an additional aspect, the invention features a system that includes agas field ion source capable of interacting with a gas to generate anion beam for a time period of one week or more with a total interruptiontime of 10 hours or less.

In one aspect, the invention features an ion microscope capable ofproducing an image of a sample. The sample is different from the ionmicroscope, and the image of the sample has a resolution of three nm orless.

In another aspect, the invention features gas field ion microscopecapable of producing an image of a sample. The sample is different fromthe ion microscope, and the image of the sample having a resolution of10 nm or less.

In a further aspect, the invention features a gas field ion microscopehaving a quality factor of 0.25 or more.

In an additional aspect, the invention features an ion microscope havinga damage test value of 25 nm or less.

In one aspect, the invention features an ion microscope that includes anion source with an electrically conductive tip having a terminal shelfwith 20 atoms or less.

In another aspect, the invention features a system that includes a gasfield ion source with an electrically conductive tip with an averagefull cone angle of from 15° to 45°.

In a further aspect, the invention features a system that includes a gasfield ion source including an electrically conductive tip with anaverage radius of curvature of 200 nm or less.

In an additional aspect, the invention features a system that includes agas field ion source having an electrically conductive tip with aterminal shelf having one or more atoms. The system is configured sothat, during use of the system, the one or more atoms interact with agas to generate an ion beam, and 70% or more of the ions in the ion beamthat reach a surface of a sample are generated via an interaction of thegas with only one atom of the one or more atoms.

In one aspect, the invention features a system that includes a gas fieldion source with an electrically conductive tip capable of interactingwith a gas to generate an ion beam. The system also includes ion opticsconfigured so that during use at least a portion of the ion beam passesthrough the ion optics. The system further includes a moving mechanismcoupled to the gas field ion source so that the moving mechanism cantranslate the electrically conductive tip, tilt the electricallyconductive tip or both.

In another aspect, the invention features a system that includes an ionsource capable of interacting with a gas to generate an ion beam thatcan interact with a sample to cause multiple different types ofparticles to leave the sample. The system also includes at least onedetector configured to detect at least two different types of particlesof the multiple different types of particles. The multiple differenttypes of particles are selected from secondary electrons, Augerelectrons, secondary ions, secondary neutral particles, primary neutralparticles, scattered ions and photons.

In a further aspect, the invention features a system that includes a gasfield ion source capable of interacting with a gas to generate an ionbeam that can interact with a sample to cause particles to leave thesample. The particles are selected from Auger electrons, secondary ions,secondary neutral particles, primary neutral particles, scattered ionsand photons. The system also includes at least one detector configuredso that, during use, the at least one detector detects at least some ofthe particles to determine information about the sample.

In an additional aspect, the invention features a system that includes agas field ion source capable of interacting with a gas to generate anion beam that can interact with a sample to cause particles to leave thesample. The system also includes at least one detector configured sothat, during use, the at least one detector can detect at least some ofthe particles. For a given detected particle, the at least one detectorproduces a signal based on an energy of the given detected particle.

In one aspect, the invention features a system that includes a gas fieldion source capable of interacting with a gas to generate an ion beamthat can interact with a sample to cause particles to leave the sample.The system also includes at least one detector configured so that,during use, the at least one detector can detect at least some of theparticles. For a given detected particle, the at least one detectorproduces a signal based on an angle of a trajectory of the givendetected particle.

In another aspect, the invention features a system that includes a gasfield ion source capable of interacting with a gas to generate an ionbeam that can interact with a sample to cause scattered ions to leavethe sample. The system also includes at least one detector configured sothat, during use, the at least one detector can detect at least some ofthe scattered ions. The system further includes an electronic processorelectrically connected to the at least one detector so that, during use,the electronic processor can process information based on the detectedscattered ions to determine information about the sample.

In a further aspect, the invention features a system that includes a gasfield ion source capable of interacting with a gas to generate an ionbeam that can interact with a sample to cause primary neutral particlesto leave the sample. The system also includes at least one detectorconfigured so that, during use, the at least one detector can detect atleast some of the primary neutral particles. The system further includesan electronic processor electrically connected to the at least onedetector so that, during use, the electronic processor can processinformation based on the detected primary neutral particles to determineinformation about the sample.

In one aspect, the invention features a system that includes a gas fieldion source capable of interacting with a gas to generate an ion beamthat can interact with a sample to cause photons to leave the sample.The system also includes at least one detector configured so that,during use, the at least one detector can detect at least some of thephotons. The system further includes an electronic processorelectrically connected to the at least one detector so that, during use,the electronic processor can process information based on the detectedphotons to determine information about the sample.

In another aspect, the invention features a system that includes a gasfield ion source capable of interacting with a gas to generate an ionbeam that can interact with a sample to cause secondary ions to leavethe sample. The system also includes at least one detector configured sothat, during use, the at least one detector can detect at least some ofthe secondary ions. The system further includes an electronic processorelectrically connected to the at least one detector so that, during use,the electronic processor can process information based on the detectedsecondary ions to determine information about the sample.

In a further aspect, the invention features a system that includes a gasfield ion source capable of interacting with a gas to generate an ionbeam that can interact with a sample to cause secondary neutralparticles to leave the sample. The system also includes at least onedetector configured so that, during use, the at least one detector candetect at least some of the secondary neutral particles. The systemfurther includes an electronic processor electrically connected to theat least one detector so that, during use, the electronic processor canprocess information based on the detected secondary neutral particles todetermine information about the sample.

In an additional aspect, the invention features a system that includes agas field ion source capable of interacting with a gas to generate anion beam that can interact with a sample to cause Auger electrons toleave the sample. The system also includes at least one detectorconfigured so that, during use, the at least one detector can detect atleast some of the Auger electrons. The system further includes anelectronic processor electrically connected to the at least one detectorso that, during use, the electronic processor can process informationbased on the detected Auger electrons to determine information about thesample.

In one aspect, the invention features a system that includes a gas fieldion source capable of interacting with a gas to generate an ion beamthat can interact with a sample to cause ions to leave the sample. Thesystem also includes at least one detector configured so that, duringuse, the at least one detector can detect the ions. The interaction ofthe ion beam with the sample may cause secondary electrons to leave thesample, and, when the interaction of the ion beam with the sample causessecondary electrons to leave the sample, the at least one detector candetect at least some of the ions without detecting the secondaryelectrons.

In another aspect, the invention features a system that includes a gasfield ion source capable of interacting with a gas to generate an ionbeam that can interact with a sample to cause neutral particles to leavethe sample. The system also includes at least one detector configured sothat, during use, the at least one detector can detect the neutralparticles. The interaction of the ion beam with the sample may causesecondary electrons to leave the sample, and, when the interaction ofthe ion beam with the sample causes secondary electrons to leave thesample, the at least one detector can detect at least some of theneutral particles without detecting the secondary electrons.

In a further aspect, the invention features a system that includes a gasfield ion source capable of interacting with a gas to generate an ionbeam that can interact with a sample to cause photons to leave thesample. The system also includes at least one detector configured sothat, during use, the at least one detector can detect the photons. Theinteraction of the ion beam with the sample may cause secondaryelectrons to leave the sample, and, when the interaction of the ion beamwith the sample causes secondary electrons to leave the sample, the atleast one detector can detect at least some of the photons withoutdetecting the secondary electrons.

In one aspect, the invention features a system that includes a gas fieldion source capable of interacting with a gas to generate an ion beamhaving a spot size with a dimension of 10 nm or less on a surface of asample. The system also includes ion optics configured to direct the ionbeam toward the surface of the sample, the ion optics having at leastone adjustable setting. When the adjustable setting of the ion opticsare at a first setting, the ion beam interacts with a first location ofthe sample. When the adjustable setting of the ion optics are at asecond setting, the ion beam interacts with a second location of thesample. The first setting of the ion optics is different from the secondsetting of the ion optics, and the first location of the sample isdifferent from the second location of the sample.

In another aspect, the invention features a system that includes a gasfield ion source capable of interacting with a gas to generate an ionbeam that is directed toward a sample. The system also includes acharged particle source configured so that, during use, the chargedparticle source provides a beam of charged particles that is directedtoward the sample. The gas field ion source is different from thecharged particle source.

In a further aspect, the invention features a method that includesinteracting an ion beam with a sample to cause multiple different typesof particles to leave the sample, and detecting at least two differenttypes of particles of the multiple different types of particles. Themultiple different types of particles are selected from secondaryelectrons, Auger electrons, secondary ions, secondary neutral particles,primary neutral particles, scattered ions and photons.

In an additional aspect, the invention features a method that includesgenerating an ion beam by interacting a gas with a gas field ion source,and interacting the ion beam with a sample to cause particles to leavethe sample. The particles are selected from Auger electrons, secondaryions, secondary neutral particles, primary neutral particles, scatteredions and photons. The method also includes detecting at least some ofthe particles to determine information about the sample.

In one aspect, the invention features a method that includes generatingan ion beam by interacting a gas with a gas field ion source, andinteracting the ion beam with a sample to cause particles to leave thesample. The method also includes producing a signal from a detectorbased on an energy of a particle detected by the detector.

In another aspect, the invention features a method that includesgenerating an ion beam by interacting a gas with a gas field ion source,and interacting the ion beam with a sample to cause particles to leavethe sample. The method also includes producing a signal from a detectorbased on an angle of a trajectory of a particle detected by thedetector.

In a further aspect, the invention features a method that includesgenerating an ion beam by interacting a gas with a gas field ion source,and interacting the ion beam with a sample to cause scattered ions toleave the sample. The method also includes detecting at least some ofthe scattered ions, and determining information about the sample basedon the detected scattered ions.

In an additional aspect, the invention features a method that includesgenerating an ion beam by interacting a gas with a gas field ion source,and interacting the ion beam with a sample to cause primary neutralparticles to leave the sample. The method also includes detecting atleast some of the primary neutral particles, and determining informationabout the sample based on the detected primary neutral particles.

In one aspect, the invention features a method that includes generatingan ion beam by interacting a gas with a gas field ion source, andinteracting the ion beam with a sample to cause photons to leave thesample. The method also includes detecting at least some of the photons,and determining information about the sample based on the detectedphotons.

In another aspect, the invention features a method that includesgenerating an ion beam by interacting a gas with a gas field ion source,and interacting the ion beam with a sample to cause secondary ions toleave the sample. The method also includes detecting at least some ofthe secondary ions.

In a further aspect, the invention features a method that includesgenerating an ion beam by interacting a gas with a gas field ion source,and interacting the ion beam with a sample to cause secondary neutralparticles to leave the sample. The method also includes detecting atleast some of the secondary neutral particles or particles derived fromthe secondary neutral particles.

In an additional aspect, the invention features a method that includesgenerating an ion beam by interacting a gas with a gas field ion source,and interacting the ion beam with a sample to cause Auger electrons toleave the sample. The method also includes detecting at least some ofthe Auger electrons.

In one aspect, the invention features a method that includes forming agas field ion source, and, after forming the gas field ion source,disposing the ion source into a chamber to provide a gas field ionsystem.

In another aspect, forming an ion source having an emission axis, and,after forming the ion source, aligning the emission axis of the ionsource with an entry axis of an ion optics system.

In a further aspect, the invention features a method that includesgenerating an ion beam by interacting a gas with a gas field ion source,the ion beam having a spot size with a dimension of 10 nm or less on asurface of a sample, and moving the ion beam from a first location onthe surface of the sample to a second location on the surface of thesample, the first location being different from the second location.

In an additional aspect, the invention features a method that includesgenerating an ion beam by interacting a gas with a gas field ion source,and contacting a sample with the ion beam. The method also includescontacting the sample with a charged particle beam from a chargedparticle source.

In one aspect, the invention features a method that includes generatingan ion beam by interacting a gas with a gas field ion source, andinteracting the ion beam with a sample to cause particles to leave thesample. The method also includes detecting at least some of theparticles, and determining crystalline information about the samplebased on the detected particles.

In another aspect, the invention features a method that includesgenerating an ion beam by interacting a gas with a gas field ion source,and inducing a voltage on a portion of the sample. The method alsoincludes detecting particles to determine voltage contrast informationabout the sample.

In a further aspect, the invention features a method that includesgenerating an ion beam by interacting a gas with a gas field ion source,and interacting the ion beam with a sample to cause particles to leavethe sample. The sample including at least a first material and a secondmaterial. The method also includes distinguishing the first and secondmaterials based on the particles.

In an additional aspect, the invention features a method that includesgenerating an ion beam by interacting a gas with a gas field ion source,and interacting the ion beam with an activating gas to promote achemical reaction at a surface of a sample.

In one aspect, the invention features a method that includes generatingan ion beam by interacting a gas with a gas field ion source, and usingthe ion beam to determine sub-surface information about a semiconductorarticle. The method also includes editing the semiconductor articlebased on the sub-surface information.

In another aspect, the invention features a method that includesgenerating an ion beam by interacting a gas with a gas field ion source,and using the ion beam to determine information about a semiconductorarticle. The ion beam has a spot size of 10 nm or less at a surface ofthe semiconductor article. The method also includes editing thesemiconductor article based on the information.

In a further aspect, the invention features a method that includesgenerating an ion beam by interacting a gas with a gas field ion source,and using the ion beam to determine information about a lithographymask. The ion beam has a spot size of 10 nm or less at a surface of thesemiconductor article. The method also includes repairing thelithography mask based on the information.

In an additional aspect, the invention features a method that includesusing an ion beam to pattern a resist on a sample. The ion beam has aspot size of 10 nm or less at the sample.

In one aspect, the invention features a method that includes generatingan ion beam by interacting a gas with a gas field ion source, andinteracting the ion beam with a sample including a feature. The ion beamhas a spot size of 50 nm or less on a surface of a sample. The methodalso includes determining the size of the feature.

In another aspect, the invention features a method that includesgenerating an ion beam by interacting a gas with a gas field ion source,and interacting the ion beam with a sample to cause particles to theleave the sample. The sample has multiple stacked layers including firstand second layers. The method also includes detecting the particles todetermine whether the second layer is registered with the first layer.

In a further aspect, the invention features a method that includesexposing a sample to a focused ion beam, and generating a second ionbeam by interacting a gas with a gas field ion source. The method alsoincludes exposing the sample to the second ion beam.

In an additional aspect, the invention features a method that includesforming an electrically conductive tip of a gas field ion source whenthe gas field ion source is present within an ion microscope.

In one aspect, the invention features a system that includes an ionsource. The system is capable of imaging the ion source in a first mode,and the system is capable of using the ion source to collect an image ofa sample in a second mode. The sample is different from the ion source.

In another aspect, the invention features a sample manipulator thatincludes a housing, a disk supported by the housing, a member supportedby the disk, the member having legs and a surface configured to supporta sample, and a device. The device contacts the member to move thesample in a first mode, and the device is not in contact with the memberin a second mode.

In an additional aspect, the invention features a system that includes agas field ion source and a sample manipulator. The sample manipulatorincludes a housing, a disk supported by the housing, a member supportedby the disk, the member having legs and a surface configured to supporta sample, and a device. The device contacts the member to move thesample in a first mode, and the device is not in contact with the memberin a second mode.

In one aspect, the invention features a method that includes generatinga first beam containing ions by interacting a gas with a gas field ionsource, and removing non-singly charged chemical species from the firstbeam to form a second beam containing singly-charged ions.

In an additional aspect, the invention features a system that includes agas field ion source capable of interacting with a gas to generate abeam comprising chemical species including charged chemical species. Thesystem also includes at least one biased electrode configured to causebeam paths of chemical species in the beam to diverge based on thecharge of the chemical species.

In another aspect, the invention features a method that includesgenerating ions by interacting a gas with a gas field ion source, andsputtering a sample with the ions.

In a further aspect, the invention features a method that includesgenerating an ion beam by interacting a gas with a gas field ion source,and generating an electron beam using a system different from the gasfield ion source. The method also includes using both the ion beam andthe electron beam to investigate a sample.

In another aspect, the invention features a system that includes ascanning electron microscope capable of providing an electron beam. Thesystem also includes a gas field ion source capable of interacting witha gas to generate an ion beam. The scanning electron microscope and thegas field ion microscope are positioned so that, during use, both theelectron beam and the ion beam can be used to investigate a sample.

In an additional aspect, the invention features a method that includesgenerating a first ion beam by interacting a gas with a gas field ionsource. The first ion beam has a first current. The method also includesusing the first ion beam having the first current to prepare the gasfield ion source for investigating a sample. The method further includesgenerating a second ion beam by interacting a gas with the gas field ionsource. The second ion beam has a second current. In addition, themethod includes using the second ion beam to investigate the sample.

Embodiments may include one or more of the following advantages.

In some embodiments, an ion source (e.g., a gas field ion source) canprovide a relatively small spot size on the surface of a sample. An ionmicroscope (e.g., a gas field ion microscope) using such an ion sourcecan, for example, obtain an image of a sample with relatively highresolution.

In certain embodiments, an ion source (e.g., a gas field ion source) canhave a relatively high brightness and/or a relatively high reducedbrightness. An ion microscope (e.g., a gas field ion microscope) usingsuch an ion source can, for example, take a good quality image of asample in a relatively short period of time, which can, in turn,increase the speed with which large numbers of samples can be imaged.

In some embodiments, an ion source (e.g., a gas field ion source) canhave a relatively high brightness for a given ion current (e.g., arelatively low etendue). An ion microscope (e.g., a gas field ionmicroscope) using such an ion source can, for example, take a goodquality image of a sample with relatively little damage to the sample.

In certain embodiments, a gas field ion microscope can have a relativelyhigh reliability. Thus, for example, the gas field ion source can beused for an extended period of time without replacing the gas field ionsource, which can, for example, increase the speed with which largenumbers of samples can be imaged, reduce the down time associated withimaging a large number of samples, and/or reduce the cost associatedwith imaging a large number of samples.

In some embodiments, an ion microscope (e.g., a gas field ionmicroscope) is configured so that vibrations are substantially decoupledfrom the ion source. This can enhance the ability of the ion microscopeto achieve one or more of the advantages noted above.

In certain embodiments, an ion microscope (e.g., a gas field ionmicroscope) can be operated at relatively high temperature while stillproviding one or more of the above-mentioned advantages. For example,liquid nitrogen can be used as the coolant for the ion microscope. Thiscan reduce the cost and/or complexity associated with using certainother coolants, such as liquid helium. This can also reduce potentialproblems associated with certain mechanical systems used with liquidhelium coolant that can create substantial vibrations.

Other features and advantages of the invention will be apparent from thedescription, drawings, and claims.

DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram of an ion microscope system.

FIG. 2 is a schematic diagram of a gas field ion source.

FIG. 3 is a schematic representation of an enlarged side view of anembodiment of a tip apex.

FIG. 4 is a schematic representation of an enlarged side view of the tipof FIG. 3.

FIG. 5 is a schematic diagram of a helium ion microscope system.

FIG. 6 is a schematic representation of an enlarged top view of anembodiment of a W(111) tip.

FIG. 7 is a schematic representation of an enlarged side view of theW(111) tip of FIG. 6.

FIG. 8 is a side view of a tip showing a cone angle measurement.

FIG. 9 is a side view of a tip showing a radius of curvaturemeasurement.

FIG. 10 is a flow chart showing an embodiment of a method of making atip.

FIG. 11A is a perspective view of an embodiment of a support assemblyfor a tip.

FIG. 11B is a bottom view of the support assembly of FIG. 11A.

FIG. 12 is a side view of an embodiment of a support assembly thatincludes a Vogel mount to support a tip.

FIG. 13 is a schematic view of an embodiment of a gas field ion sourceand ion optics.

FIG. 14 is a schematic view of an embodiment of an ion optical system.

FIG. 15 is a top view of an embodiment of a multi-opening aperture.

FIG. 16 is a top view of an embodiment of a multi-opening aperture.

FIG. 17 is a cross-sectional view of an embodiment of a movementmechanism for a gas field ion microscope tip.

FIG. 18 is a schematic diagram of an Everhart-Thomley detector.

FIG. 19 is a cross-sectional view of a portion of a gas field ionmicroscope system including a microchannel plate detector.

FIGS. 20A and 20B are side and top views of a gold island supported by acarbon surface.

FIG. 20C is a plot of average measured secondary electron totalabundance as a function of ion beam position for the sample of FIGS. 20Aand 20B.

FIG. 21 is a schematic diagram of a portion of a gas field ionmicroscope including a gas delivery system.

FIG. 22 is a schematic diagram of a portion of a gas field ionmicroscope including a flood gun.

FIG. 23 is a schematic diagram of a sample including a sub-surfacecharge layer.

FIG. 24 is a schematic diagram of a collector electrode for reducingsurface charge on a sample.

FIG. 25 is a schematic diagram of a flood gun apparatus for reducingsurface charge on a sample.

FIG. 26 is a schematic diagram of a flood gun apparatus including aconversion plate for reducing surface charge on a sample.

FIG. 27A is a schematic representation of a sample having a positivelycharged layer disposed therein.

FIG. 27B is a schematic representation of a sample having positively andnegatively charged layers disposed therein.

FIG. 28 is a schematic diagram of an embodiment of a vibration-decoupledsample manipulator.

FIG. 29 is a schematic diagram of an embodiment of a vibration-decoupledsample manipulator.

FIG. 30 is a schematic diagram of an embodiment of a vibration-decoupledsample manipulator.

FIG. 31 is a schematic diagram of an electrostatic filtering system forseparating ions and neutral atoms in a particle beam.

FIG. 32 is a schematic diagram of an electrostatic filtering system forseparating neutral atoms, singly-charged ions, and doubly-charged ionsin a particle beam.

FIG. 33 is a schematic diagram of a filtering system that includes adispersionless sequence of electric and magnetic fields for separatingneutral atoms, singly-charged ions, and doubly-charged ions in aparticle beam.

FIG. 34A is a schematic diagram showing an embodiment of helium ionscattering patterns from a surface.

FIG. 34B is a diagram showing plots of the relative abundance ofscattered helium ions detected by the detectors in FIG. 34A.

FIGS. 35A, 35D and 35G are schematic diagrams showing respectiveembodiments of helium ion scattering patterns from a surface usingdifferent detectors to detect the scattered helium ions.

FIGS. 35B, 35E and 35H are plots of the total scattered helium ion yieldfor the systems shows in FIGS. 35A, 35D and 35G, respectively.

FIGS. 35C, 35F and 35I are plots of the relative abundance of scatteredhelium ions detected by the detectors in FIGS. 35A, 35D and 35G,respectively.

FIG. 36 is a schematic diagram showing a portion of a gas field ionmicroscope including an arrangement of detectors for measuring scatteredions from a sample.

FIGS. 37A-37D are scanning electron microscope images an electricallyconductive tip.

FIG. 38 is a digitized representation of the surface of an electricallyconductive tip.

FIG. 39 is a plot of the slope of the slope of the surface shown in FIG.38.

FIG. 40 is a field ion microscope image of an electrically conductivetip having a trimer as the terminal shelf at its apex.

FIG. 41 is a scanning field ion microscope image of an electricallyconductive tip having a trimer as the terminal shelf at its apex.

FIG. 42 is an image of a sample taken with a helium ion microscopeconfigured to detect secondary electrons.

FIG. 43 is an image of a sample taken with a helium ion microscopeconfigured to detect secondary electrons.

FIG. 44 is a scanning field ion microscope image of an electricallyconductive tip.

FIG. 45 is a field ion microscope image of an electrically conductivetip having a trimer as the terminal shelf at its apex.

FIG. 46 is a scanning electron microscope image of an electricallyconductive tip.

FIG. 47 is a field ion microscope image of an electrically conductivetip.

FIG. 48 is a field ion microscope image of an electrically conductivetip.

FIG. 49 is a field ion microscope image of an electrically conductivetip.

FIG. 50 is a scanning field ion microscope image of an electricallyconductive tip having a trimer as the terminal shelf at its apex.

FIG. 51 is an image of a sample taken with a helium ion microscopeconfigured to detect secondary electrons.

FIG. 52 is an image of a sample taken with a helium ion microscopeconfigured to detect secondary electrons.

FIG. 53 is an image of a sample taken with a helium ion microscopeconfigured to detect secondary electrons.

FIG. 54 is an image of a sample taken with a helium ion microscopeconfigured to detect secondary electrons.

FIG. 55 is an image of a sample taken with a helium ion microscopeconfigured to detect secondary electrons.

FIG. 56 is a schematic representation of a support for a tip.

FIG. 57 is a schematic representation of a support for a tip.

FIG. 58 is an image of a sample taken with a helium ion microscopeconfigured to detect secondary electrons.

FIG. 59A is an image of a sample taken with a helium ion microscopeconfigured to detect secondary electrons.

FIG. 59B is an image of a sample taken with a scanning electronmicroscope.

FIG. 60 is a graph of secondary electron current from a sample.

FIG. 61A is an image of a sample taken with a helium ion microscopeconfigured to detect secondary electrons.

FIG. 61B is an image of a sample taken with a scanning electronmicroscope.

FIG. 62 is an image of a sample taken with a helium ion microscopeconfigured to detect secondary electrons.

FIG. 63 is an image of a sample taken with a helium ion microscopeconfigured to detect secondary electrons.

FIG. 64 is an image of a sample taken with a helium ion microscopeconfigured to detect secondary electrons.

FIG. 65 is an image of a sample taken with a helium ion microscopeconfigured to detect secondary electrons.

FIG. 66 is an embodiment of a detector configuration configured todetect secondary electrons.

FIG. 67A is a graph of secondary electron intensity at varying samplelocations based on the image in FIG. 59A.

FIG. 67B is a graph of secondary electron intensity at varying samplelocations based on the image in FIG. 59B.

FIG. 68 is an image of a sample taken with a helium ion microscopeconfigured to detect helium ions and neutral helium atoms.

FIGS. 69A-69C are images of a sample taken with a helium ion microscopeconfigured to detect helium ions and neutral helium atoms.

FIG. 70A is an image of a sample taken with a helium ion microscopeconfigured to detect helium ions and neutral helium atoms.

FIG. 70B is a polar plot showing the angular intensity of helium ionsand helium atoms leaving the sample for the image of FIG. 70A.

FIG. 71A is an image of a sample taken with a helium ion microscopeconfigured to detect helium ions and neutral helium atoms.

FIG. 71B is a polar plot showing the angular intensity of helium ionsand helium atoms leaving the sample for the image of FIG. 71A.

FIG. 72 is an image of a sample taken with a helium ion microscopeconfigured to detect helium ions and neutral helium atoms.

FIG. 73 is an image of a sample taken with a helium ion microscopeconfigured to detect helium ions and neutral helium atoms.

FIG. 74 is an image of a sample taken using a helium ion microscopeconfigured to detect photons.

FIG. 75 is an image of a sample taken with a helium ion microscopeconfigured to detect secondary electrons.

FIG. 76 is an expanded view of a portion of the image of FIG. 75.

FIG. 77 is a plot of image intensity as a function of pixel position fora line scan through the image of FIG. 76.

FIG. 78 is a plot of the data shown in FIG. 77 after numerical scalingand smoothing operations.

FIG. 79 is an image of a sample taken with a helium ion microscopeconfigured to detect helium ions and neutral helium atoms.

FIG. 80 is a plot of image intensity as a function of pixel position fora line scan through a portion of the image of FIG. 79.

FIG. 81 is an image of a sample taken with a scanning electronmicroscope.

FIG. 82 is a plot of image intensity as a function of pixel position fora line scan through a portion of the image of FIG. 81.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

General Introduction

Ions can be produced and used for sample imaging and other applicationsin microscope systems. Microscope systems that use a gas field ionsource to generate ions that can be used in sample analysis (e.g.,imaging) are referred to as gas field ion microscopes. A gas field ionsource is a device that includes an electrically conductive tip(typically having an apex with 10 or fewer atoms) that can be used toionize neutral gas species to generate ions (e.g., in the form of an ionbeam) by bringing the neutral gas species into the vicinity of theelectrically conductive tip (e.g., within a distance of about four tofive angstroms) while applying a high positive potential (e.g., one kVor more relative to the extractor (see discussion below)) to the apex ofthe electrically conductive tip.

FIG. 1 shows a schematic diagram of a gas field ion microscope system100 that includes a gas source 110, a gas field ion source 120, ionoptics 130, a sample manipulator 140, a front-side detector 150, aback-side detector 160, and an electronic control system 170 (e.g., anelectronic processor, such as a computer) electrically connected tovarious components of system 100 via communication lines 172 a-172 f. Asample 180 is positioned in/on sample manipulator 140 between ion optics130 and detectors 150, 160. During use, an ion beam 192 is directedthrough ion optics 130 to a surface 181 of sample 180, and particles 194resulting from the interaction of ion beam 192 with sample 180 aremeasured by detectors 150 and/or 160.

In general, it is desirable to reduce the presence of certainundesirable chemical species in system 100 by evacuating the system.Typically, different components of system 100 are maintained atdifferent background pressures. For example, gas field ion source 120can be maintained at a pressure of approximately 10⁻¹⁰ Torr. When gas isintroduced into gas field ion source 120, the background pressure risesto approximately 10⁻⁵ Torr. Ion optics 130 are maintained at abackground pressure of approximately 10⁻⁸ Torr prior to the introductionof gas into gas field ion source 120. When gas is introduced, thebackground pressure in ion optics 130 typically increase toapproximately 10⁻⁷ Torr. Sample 180 is positioned within a chamber thatis typically maintained at a background pressure of approximately 10⁻⁶Torr. This pressure does not vary significantly due to the presence orabsence of gas in gas field ion source 120.

As shown in FIG. 2, gas source 110 is configured to supply one or moregases 182 to gas field ion source 120. As described in more detailbelow, gas source 110 can be configured to supply the gas(es) at avariety of purities, flow rates, pressures, and temperatures. Ingeneral, at least one of the gases supplied by gas source 110 is a noblegas (helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe)), andions of the noble gas are desirably the primary constituent in ion beam192. In general, as measured at surface 181 of sample 180, the currentof ions in ion beam 192 increases monotonically as the pressure of thenoble gas in system 100 increases. In certain embodiments, thisrelationship can be described by a power law where, for a certain rangeof noble gas pressures, the current increases generally in proportion togas pressure. During operation, the pressure of the noble gas istypically 10⁻² Torr or less (e.g., 10⁻³ Torr or less, 10⁻⁴ Torr orless), and/or 10⁻⁷ Torr or more (e.g., 10⁻⁶ Torr or more, 10⁻⁵ Torr ormore) adjacent the tip apex (see discussion below). In general, it isdesirable to use relatively high purity gases (e.g., to reduce thepresence of undesirable chemical species in the system). As an example,when He is used, the He can be at least 99.99% pure (e.g., 99.995% pure,99.999% pure, 99.9995% pure, 99.9999% pure). Similarly, when other noblegases are used (Ne gas, Ar gas, Kr gas, Xe gas), the purity of the gasesis desirably high purity commercial grade.

Optionally, gas source 110 can supply one or more gases in addition tothe noble gas(es). As discussed in more detail below, an example of sucha gas is nitrogen. Typically, while the additional gas(es) can bepresent at levels above the level of impurities in the noble gas(es),the additional gas(es) still constitute minority components of theoverall gas mixture introduced by gas source 110. As an example, inembodiments in which He gas and Ne gas are introduced by gas source 110into gas field ion source 120, the overall gas mixture can include 20%or less (e.g., 15% or less, 12% or less) Ne, and/or 1% or more (e.g., 3%or more, 8% or more) Ne. For example, in embodiments in which He gas andNe gas are introduced by gas source 110, the overall gas mixture caninclude from 5% to 15% (e.g., from 8% to 12%, from 9% to 11%) Ne. Asanother example, in embodiments in which He gas and nitrogen gas areintroduced by gas source 110, the overall gas mixture can include 1% orless (e.g., 0.5% or less, 0.1% or less) nitrogen, and/or 0.01% or more(e.g., 0.05% or more) nitrogen. For example, in embodiments in which Hegas and nitrogen gas are introduced by gas source 110, the overall gasmixture can include from 0.01% to 1% (e.g., from 0.05% to 0.5%, from0.08 to 0.12%) nitrogen. In some embodiments, the additional gas(es) aremixed with the noble gas(es) before entering system 100 (e.g., via theuse of a gas manifold that mixes the gases and then delivers the mixtureinto system 100 through a single inlet). In certain embodiments, theadditional gas(es) are not mixed with the noble gas(es) before enteringsystem 100 (e.g., a separate inlet is used for inputting each gas intosystem 100, but the separate inlets are sufficiently close that thegases become mixed before interacting with any of the elements in gasfield ion source 120).

Gas field ion source 120 is configured to receive the one or more gases182 from gas source 110 and to produce gas ions from gas(es) 182. Gasfield ion source 120 includes an electrically conductive tip 186 with atip apex 187, an extractor 190 and optionally a suppressor 188.Typically, the distance from tip apex 187 to surface 181 of sample 180(not shown in FIG. 2) is five cm or more (e.g., 10 cm or more, 15 cm ormore, 20 cm or more, 25 cm or more), and/or 100 cm or less (e.g., 80 cmor less, 60 cm or less, 50 cm or less). For example, in someembodiments, the distance from tip apex 187 to surface 181 of sample 180is from five cm to 100 cm (e.g., from 25 cm to 75 cm, from 40 cm to 60cm, from 45 cm to 55 cm).

Electrically conductive tip 186 can be formed of various materials. Insome embodiments, tip 186 is formed of a metal (e.g., tungsten (W),tantalum (Ta), iridium (Ir), rhenium (Rh), niobium (Nb), platinum (Pt),molybdenum (Mo)). In certain embodiments, electrically conductive tip186 can be formed of an alloy. In some embodiments, electricallyconductive tip 186 can be formed of a different material (e.g., carbon(C)).

During use, tip 186 is biased positively (e.g., approximately 20 kV)with respect to extractor 190, extractor 190 is negatively or positivelybiased (e.g., from −20 kV to +50 kV) with respect to an external ground,and optional suppressor 188 is biased positively or negatively (e.g.,from −5 kV to +5 kV) with respect to tip 186. Because tip 186 is formedof an electrically conductive material, the electric field of tip 186 attip apex 187 points outward from the surface of tip apex 187. Due to theshape of tip 186, the electric field is strongest in the vicinity of tipapex 187. The strength of the electric field of tip 186 can be adjusted,for example, by changing the positive voltage applied to tip 186. Withthis configuration, un-ionized gas atoms 182 supplied by gas source 110are ionized and become positively-charged ions in the vicinity of tipapex 187. The positively-charged ions are simultaneously repelled bypositively charged tip 186 and attracted by negatively charged extractor190 such that the positively-charged ions are directed from tip 186 intoion optics 130 as ion beam 192. Suppressor 188 assists in controllingthe overall electric field between tip 186 and extractor 190 and,therefore, the trajectories of the positively-charged ions from tip 186to ion optics 130. In general, the overall electric field between tip186 and extractor 190 can be adjusted to control the rate at whichpositively-charged ions are produced at tip apex 187, and the efficiencywith which the positively-charged ions are transported from tip 186 toion optics 130.

As an example, without wishing to be bound by theory, it is believedthat He ions can be produced as follows. Gas field ion source 120 isconfigured so that the electric field of tip 186 in the vicinity of tipapex 187 exceeds the ionization field of the un-ionized He gas atoms182, and tip 186 is maintained at a relatively low temperature. When theun-ionized He gas atoms 182 are in close proximity to tip apex 187, theHe atoms can be polarized by the electric field of the tip, producing aweakly attractive force between He atoms 182 and tip apex 187. As aresult, He atoms 182 may contact tip apex 187 and remain bound (e.g.,physisorbed) thereto for some time. In the vicinity of tip apex 187, theelectric field is high enough to ionize He atoms 182 adsorbed onto tipapex 187, generating positively charged He ions (e.g., in the form of anion beam).

FIG. 3 is a schematic representation of tip apex 187 (formed of W(111),see discussion below). Tip apex 187 includes layers of atoms arranged toform atomic shelves. A terminal atomic shelf is formed by atoms 142. Asecond atomic shelf is formed by atoms 144, and a third atomic shelf isformed by atoms 146. Neutral gas atoms 182 delivered by gas source 110are present in the vicinity of tip apex 187. Atoms 182 become polarizeddue to the electric field of tip apex 187, and experience a relativelyweak attractive force that causes atoms 182 to move towards tip apex187, as indicated by the arrows on atoms 182.

Depending upon the strength of the tip's electric field, each atoms inthe atomic shelves near tip apex 187 can have a corresponding ionizationdisk 148. An ionization disk 148 is a region of space in which a neutralHe atom, venturing thereinto, has a high probability of undergoingionization. Typically, ionization of a neutral He atom occurs viaelectron tunneling from the neutral He atom to a tip apex atom.Ionization disks 148 therefore represent spatial regions in which Heions are generated, and from which the He ions emerge.

The sizes of the ionization disks 148 for particular tip apex atoms aredependent upon the shape of tip apex 187 and the electrical potentialapplied to tip apex 187. In general, ionization of He atoms can occur inspatial regions adjacent to tip apex 187 where the local electric fieldexceeds the ionization potential of He atoms. For a large electricpotential applied to tip apex 187, therefore, many tip atoms will haveionization disks. In addition, the local electric field in the vicinityof tip apex 187 depends upon the shape of tip apex 187. For a relativelysharp tip apex, the local electric field in the vicinity of tip apex 187will be relatively high. For a relatively blunt tip apex, the localelectric field, even in the vicinity of tip apex 187, will be smaller.

Ionization disks 148 corresponding to individual atoms of tip apex 187are spatially separated from one another in FIG. 3. In some embodiments,if the electric field of tip apex 187 is sufficiently large, ionizationdisks from more than one atom (e.g., atoms 142) can overlap spatially,creating a larger ionization disk that spans a region of space proximalto multiple tip apex atoms. By reducing the electric field at tip apex187, the volume of space occupied by ionization disks 148 can bereduced, and the geometry depicted in FIG. 3 can be realized where a fewtip apex atoms each have their own individual, spatially separatedionization disks. Because, in many instances, the shape of tip apex 187is not easily altered during use of ion source 120, the electric fieldin the vicinity of tip apex 187 is typically controlled by adjusting theelectrical potential applied to tip apex 187.

By further reducing the potential applied to tip apex 187, some of theionization disks in FIG. 3 can be eliminated. For example, tip apex 187is not as sharp in the vicinity of second atomic shelf atoms 144, and byreducing the potential applied to tip apex 187, the electric field oftip apex 187 in the vicinity of atoms 144 can be reduced so that He atomionization does not occur with high probability in these regions. As aresult, ionization disks corresponding to atoms 144 are no longerpresent. However, the electric field of tip apex 187 in the vicinity ofterminal shelf atoms 142 can still be high enough to cause He atomionization, and so ionization disks 148 corresponding to atoms 142remain. By carefully controlling the electrical potential applied to tipapex 187, ion source 120 can operate so that the only ionization diskspresent correspond to terminal shelf atoms 142, and the ionization diskscorresponding to the terminal shelf atoms are spatially separated fromone another. As a result, a He atom that is ionized in the vicinity oftip apex 187 is produced via ionization in the vicinity of a particularterminal shelf atom.

Neutral He atoms 182 have a higher probability of undergoing ionizationthe longer they remain within ionization disks 148. The polarization ofHe atoms which is induced by the electric field of tip apex 187, andwhich causes polarized He atoms to move toward tip apex 187, furtherensures that the polarized He atoms remain bound to tip apex 187,increasing the amount of time that the He atoms 182 remain withinionization disks 148, and increasing the probability of ionization ofthe polarized He atoms over time.

Polarized He atoms can also move from one position to another along thesurface of tip apex 187. Because the attractive force between apolarized He atom and tip apex 187 depends on the local strength of theelectric field of tip apex 187 at the position of the polarized He atom,the motion of polarized He atoms tends to transport the atoms toward theend of tip apex 187 of tip 186 (e.g., toward terminal shelf 142) wherethe local electric field is highest. This transport mechanism ofpolarized He atoms, in combination with control over the electricalpotential applied to tip 186 (e.g., to ensure that discrete ionizationdisks corresponding to only terminal shelf atoms 142 are present), canbe used to operate ion source 120 such that a He ion beam 192 isproduced by gas field ionization source 120, where individual He ions inthe ion beam are generated via the interaction of He gas with one of theterminal shelf atoms 142. Ion beam 192 therefore includes a plurality ofHe ions from each of the terminal shelf atoms 142, where each He ion canbe attributed to ionization at one of the terminal shelf atoms 142.

As discussed above, in general, the size and shape of ionization disks148 can be modified by changing the electrical potential applied to tipapex 187, and adjacent ionization disks 148 can be made to overlap witha suitably large applied potential, or maintained spatially distinctfrom one another by a suitably small applied potential. Typically,ionization disks 148 are spaced from tip atoms 142, 144, and 146 by adistance of approximately 0.4 nm. Individual ionization diskscorresponding to tip atoms typically have a thickness of approximately0.02 nm, measured in a direction along a line joining a given disk andits corresponding atom. Ionization disks 148 typically have a diameter,measured in a direction normal to the line joining a given disk and itscorresponding atom, of approximately the diameter of the correspondingatom.

FIG. 4 shows an operating configuration of tip apex 187 where theelectrical potential applied to tip 186 produces three ionization disks148, each of which corresponds to one of three terminal atomic shelfatoms 142. Once He ions are produced in the vicinity of tip apex 187,they are rapidly accelerated away from the tip due to the large positivetip potential. He ions are accelerated away from tip apex 187 along aplurality of trajectories. Two such trajectories 156 are shown in FIG.4. As depicted in FIG. 4, trajectories 156 correspond to the left- andright-hand limits of the full width at half maximum (FWHM) trajectorydistribution for the middle terminal shelf atom. As such, iftrajectories 156 are extrapolated backwards (e.g., along lines 154) tothe position of the middle terminal shelf atom, they define a virtualsource 152 for the middle terminal shelf atom. The diameter of virtualsource 152 is typically smaller than the diameter of the middle terminalshelf atom, and may be much smaller than the diameter of the middleterminal shelf atom (e.g., by a factor of 2 or more, a factor of 3 ormore, a factor of 5 or more, a factor of 10 or more). Similarconsiderations apply to the other terminal shelf atoms, and eachterminal shelf atom has a corresponding virtual source size.

The small virtual source size for terminal shelf atoms can provide anumber of advantages. For example, the small virtual source size of ionbeam 192 and the relatively small thickness of the ionization disk 148from which ions in ion beam 192 arise can assist in ensuring that ionbeam 192 has a relatively high brightness and a relatively narrow ionenergy distribution.

Without wishing to be bound by theory, it is believed that using a tiptemperature that is too low can negatively impact current stabilityand/or increase undesirable effects from increased impurity adsorptionon the tip. In general, the temperature of tip 186 is 5 K or more (e.g.,10 K or more, 25 K or more, 50 K or more 75 K or more), and/or 100 K orless (e.g., 90 K or less, 80 K or less). For example, the temperature oftip 186 can be from 5 K to 100 K (e.g., from 25 K to 90 K, from 50 K to90 K, from 75 K to 80K). The temperature of tip 186 can be attained bythermal coupling with a coolant, such as, for example, liquid helium orliquid nitrogen. Alternatively or additionally, tip 186 can be thermallycooled using a cryogenic refrigerator.

It is believed that, if the temperature of tip 186 is too low, the rateat which adsorbed He atoms are transported by moving to atoms 142 in theterminal atomic shelf of tip apex 187 is reduced so that not enough Heatoms per unit time reach atoms 142 where they can be ionized. As aresult, when the emission pattern of tip 186 is observed (e.g., by usingfield ion microscope (FIM) techniques, or by scanning FIM (SFIM)techniques), the abundance of ions from individual terminal shelf atomsalternates from relatively high abundance to relatively low abundance(commonly referred to as blinking). This can occur, for example, whenthere are no He atoms available for ionization in the vicinity of theterminal shelf atom at certain times. As the temperature of tip 186 isincreased, the transport rate of He atoms toward the terminal shelf ofatoms of tip apex 187 increases, and the observation of this alternatinghigh/low abundance from terminal shelf atoms 142 is reduced oreliminated.

It is also believed that, if the temperature of tip 186 is too high,polarized He atoms will have too much kinetic energy to remain bound totip 186 for sufficiently long periods of time to ensure efficientionization of He atoms in the vicinity of terminal shelf atoms 142. Thiscan also result in disappearance of the emission pattern from individualterminal shelf atoms as observed using FIM and/or SFIM imagingtechniques. As a result, to ensure that the He ionization process ateach of the terminal shelf atoms 142 produces stable ion currents fromeach of the terminal shelf atoms 142, the temperature of tip 186 iscarefully controlled to mitigate against both undesirable high- andlow-temperature effects.

In general, ion optics 130 are configured to direct ion beam 192 ontosurface 181 of sample 180. As described in more detail below, ion optics130 can, for example, focus, collimate, deflect, accelerate, and/ordecelerate ions in beam 192. Ion optics 130 can also allow only aportion of the ions in ion beam 192 to pass through ion optics 130.Generally, ion optics 130 include a variety of electrostatic and otherion optical elements that are configured as desired. By manipulating theelectric field strengths of one or more components (e.g., electrostaticdeflectors) in ion optics 130, He ion beam 192 can be scanned acrosssurface 181 of sample 180. For example, ion optics 130 can include twodeflectors that deflect ion beam 192 in two orthogonal directions. Thedeflectors can have varying electric field strengths such that ion beam192 is rastered across a region of surface 181.

When ion beam 192 impinges on sample 180, a variety of different typesof particles 194 can be produced. These particles include, for example,secondary electrons, Auger electrons, secondary ions, secondary neutralparticles, primary neutral particles, scattered ions and photons (e.g.,X-ray photons, IR photons, visible photons, UV photons). Detectors 150and 160 are positioned and configured to each measure one or moredifferent types of particles resulting from the interaction between Heion beam 192 and sample 180. As shown in FIG. 1, detector 150 ispositioned to detect particles 194 that originate primarily from surface181 of sample 180, and detector 160 is positioned to detect particles194 that emerge primarily from surface 183 of sample 180 (e.g.,transmitted particles). As described in more detail below, in general,any number and configuration of detectors can be used in the microscopesystems disclosed herein. In some embodiments, multiple detectors areused, and some of the multiple detectors are configured to measuredifferent types of particles. In certain embodiments, the detectors areconfigured to provide different information about the same type ofparticle (e.g., energy of a particle, angular distribution of a givenparticle, total abundance of a given particle). Optionally, combinationsof such detector arrangements can be used.

In general, the information measured by the detectors is used todetermine information about sample 180. Exemplary information aboutsample 180 includes topographical information about surface 181,material constituent information (of surface 181 and/or of a sub-surfaceregion of sample 180), crystalline orientation information of sample180, voltage contrast information about (and therefore electricalproperties of) surface 181, voltage contrast information about asub-surface region of sample 180, optical properties of sample 180,and/or magnetic properties of sample 180. Typically, this information isdetermined by obtaining one or more images of sample 180. By rasteringion beam 192 across surface 181, pixel-by-pixel information about sample180 can be obtained in discrete steps. Detectors 150 and/or 160 can beconfigured to detect one or more different types of particles 194 ateach pixel. Typically, a pixel is a square, although in someembodiments, pixels can have different shapes (e.g., rectangular). Apixel size, which corresponds to a length of a side of the pixel, canbe, for example, from 100 pm to two μm (e.g., from one nm to one μm). Insome embodiments, the location of adjacent pixels can be determined towithin at least 200 pm (e.g., to within at least 100 pm, to within atleast 75 pm, to within at least 50 pm). Thus, the operator of the systemcan determine the location of the center of the beam spot to within atleast 200 pm (e.g., to within at least 100 pm, to within at least 75 pm,to within at least 50 pm). In certain embodiments, the field of view(FOV) of sample 180 is 200 nm or more (e.g., 500 nm or more, 1 μm ormore, 50 μm or more, 100 μm or more, 500 μm or more, 1 mm or more, 1.5mm or more), and/or 25 mm or less (15 mm or less, 10 mm or less, five mmor less). The field of view refers to the area of a sample surface thatis imaged by the ion microscope.

The operation of microscope system 100 is typically controlled viaelectronic control system 170. For example, electronic control system170 can be configured to control the gas(es) supplied by gas source 110,the temperature of tip 186, the electrical potential of tip 186, theelectrical potential of extractor 190, the electrical potential ofsuppressor 188, the settings of the components of ion optics 130, theposition of sample manipulator 140, and/or the location and settings ofdetectors 150 and 160. Optionally, one or more of these parameters maybe manually controlled (e.g., via a user interface integral withelectronic control system 170). Additionally or alternatively,electronic control system 170 can be used (e.g., via an electronicprocessor, such as a computer) to analyze the information collected bydetectors 150 and 160 and to provide information about sample 180 (e.g.,topography information, material constituent information, crystallineinformation, voltage contrast information, optical property information,magnetic information), which can optionally be in the form of an image,a graph, a table, a spreadsheet, or the like. Typically, electroniccontrol system 170 includes a user interface that features a display orother kind of output device, an input device, and a storage medium.

Helium Ion Microscope Systems

A. Overview

FIG. 5 shows a schematic diagram of a He ion microscope system 200.Microscope system 200 includes a first vacuum housing 202 enclosing a Heion source and ion optics 130, and a second vacuum housing 204 enclosingsample 180 and detectors 150 and 160. Gas source 110 delivers He gas tomicroscope system 200 through a delivery tube 228. A flow regulator 230controls the flow rate of He gas through delivery tube 228, and atemperature controller 232 controls the temperature of He gas in gassource 110. The He ion source includes a tip 186 affixed to a tipmanipulator 208. The He ion source also includes an extractor 190 and asuppressor 188 that are configured to direct He ions from tip 186 intoion optics 130. Ion optics 130 include a first lens 216, alignmentdeflectors 220 and 222, an aperture 224, an astigmatism corrector 218,scanning deflectors 219 and 221, and a second lens 226. Aperture 224 ispositioned in an aperture mount 234. Sample 180 is mounted in/on asample manipulator 140 within second vacuum housing 204. Detectors 150and 160, also positioned within second vacuum housing 204, areconfigured to detect particles 194 from sample 180. Gas source 110, tipmanipulator 208, extractor 190, suppressor 188, first lens 216,alignment deflectors 220 and 222, aperture mount 234, astigmatismcorrector 218, scanning deflectors 219 and 221, sample manipulator 140,and/or detectors 150 and/or 160 are typically controlled by electroniccontrol system 170. Optionally, electronic control system 170 alsocontrols vacuum pumps 236 and 237, which are configured to providereduced-pressure environments inside vacuum housings 202 and 204, andwithin ion optics 130.

B. Ion Source

As noted above, in general, tip 186 can be formed of any appropriateelectrically conductive material. In certain embodiments, tip 186 can beformed of a single crystal material, such as a single crystal metal.Typically, a particular single crystal orientation of the terminal shelfof atoms of tip apex 187 is aligned with a longitudinal axis of tip 186to within 3° or less (e.g., within 2° or less, within 1° or less). Insome embodiments, apex 187 of tip 186 can terminate in an atomic shelfhaving a certain number of atoms (e.g., 20 atoms or less, 15 atoms orless, 10 atoms or less, nine atoms or less, six atoms or less, threeatoms or less). For example, apex 187 of tip 186 can be formed of W(111)and can have a terminal shelf with three atoms (a trimer). FIGS. 6 and 7show schematic representations of enlarged top and side views,respectively, of the two atomic shelves of a W tip 186 that are nearestto the apex of tip. The terminal shelf, which includes three W atoms 302arranged in a trimer, corresponds to a (111) surface of W. Withoutwishing to be bound by theory, it is believed that this trimer surfaceis advantageous (in terms of its ease of formation, reformation andstability) because the surface energy of the W(111) crystal facefavorably supports a terminal shelf formed by three W atoms arranged inan equilateral triangle to form a trimer. The trimer atoms 302 aresupported by a second shelf of W atoms 304.

In some embodiments, tip 186 can have a terminal shelf that includesfewer than three atoms or more than three atoms. For example, a W(111)tip can have a terminal shelf that includes two atoms, or a terminalshelf that includes only one atom. Alternatively, a W(111) tip can havea terminal shelf that includes four or more atoms (e.g., five or moreatoms, six or more atoms, seven or more atoms, eight or more atoms, nineor more atoms, ten or more atoms, more than ten atoms).

Alternatively, or in addition, tips that correspond to other Wcrystalline orientations (e.g., W(112), W(110) or W(100)) can be used,and such tips can have terminal shelves that include one or more atoms(e.g., two or more atoms, three or more atoms, four or more atoms, fiveor more atoms, six or more atoms, seven or more atoms, eight or moreatoms, nine or more atoms, ten or more atoms, more than ten atoms).

In some embodiments, tips formed from a material other than singlecrystal W can be used in the ion source (e.g., a single crystal of ametal, such as a single crystal of one of the metals noted above), andsuch tips can have terminal shelves that include one or more atoms(e.g., two or more atoms, three or more atoms, four or more atoms, fiveor more atoms, six or more atoms, seven or more atoms, eight or moreatoms, nine or more atoms, ten or more atoms, more than ten atoms).

As described below, the shape of tip apex 187 can have an impact on thequality of the ion beam, which can have an impact on the performance ofmicroscope system 200. For example, when viewed from the side, tip apex187 can be symmetrically formed about its longitudinal axis, or it canbe asymmetrically formed about its longitudinal axis. In certainembodiments, from one or more side views, tip apex 187 may besymmetrically formed about its longitudinal axis, and, from one or moredifferent side views, tip apex 187 may be asymmetrically formed aboutits longitudinal axis. FIG. 8 shows a side view of an exemplary tip 300(at much smaller magnification than in FIGS. 6 and 7) that isasymmetrically formed with respect to its longitudinal axis 308. From agiven side view, the degree to which tip 300 is asymmetrically formedalong longitudinal axis 308 can be quantified using parameters such as,for example, an average full cone angle and an average cone direction.These parameters are determined as follows.

An image of tip 300 is obtained using a scanning electron microscope(SEM). FIG. 8 is a schematic representation of such an image. Tip 300includes an apex point 310 and a second point 312, both located onlongitudinal axis 308, with point 312 spaced one μm from apex point 310along longitudinal axis 308. An imaginary line 314 extends perpendicularto axis 308 and through point 312 in the plane of FIG. 8. Line 314intersects the profile of tip 300 at points 316 and 318. The left coneangle θ_(l) is the angle between the tangent to the profile of tip 300at point 316 and line 320 (an imaginary line through point 316 andextending parallel to axis 308). Similarly, the right cone angle θ_(r)is the angle between the tangent to the profile of tip 300 at point 318and line 322 (an imaginary line through point 318 and extending parallelto axis 308). The full cone angle of tip 300 is the sum of themagnitudes of θ_(l) and θ_(r). For example, for a given side view in anembodiment in which the magnitude of θ_(l) is 21.3° and the magnitude ofθ_(r) is 11.6°, the full cone angle for the profile of tip 300 for thatside view 32.9°. Because tip 300 can appear symmetric in one side viewand asymmetric in a different side view, it is generally desirable todetermine an average full cone angle for tip 300. The average full coneangle is determined by measuring the full cone angle for eight differentside views of tip 300 (each corresponding to a successive rotation oftip 300 by 45° about axis 308 with respect to the previous side view oftip 300), and then calculating the average of the eight full cone anglesthus determined, resulting in the average full cone angle. Withoutwishing to be bound by theory, it is believed that if the average fullcone angle is too small, arcing may occur during use of the tip (e.g.,when tip 300 is used to produce ion beam 192), and generation of He ionsvia the interaction He atoms with tip atoms other than those on theterminal shelf of the tip may occur due to large electric fields in thevicinity of tip 300. It is also believed that, if the average full coneangle is too large, the ability to reproducibly re-build tip 300 can bereduced, and electric fields in the vicinity of tip 300 may be too lowto reliably ionize He atoms and produce a stable He ion current. In someembodiments, the average full cone angle of tip 300 can be 45° or less(e.g., 42° or less, 40° or less, 35° or less, 32° or less, 31° or less),and/or the average full cone angle can be 15° or more (e.g., 20° ormore, 23° or more, 25° or more, 28° or more, 29° or more). For example,the average full cone angle of tip 300 can be from 27° to 33° (e.g.,from 28° to 32°, from 29° to 31°, 30°). In certain embodiments, thestandard deviation of the eight full cone angle measurements is 40% orless (e.g., 30% or less, 20% or less, 10% or less) of the average fullcone angle.

The cone direction is half of the absolute value of the differencebetween the magnitudes of θ_(l) and θ_(r). Thus, for example, for agiven side view in an embodiment in which the magnitude of θ_(l) is21.3° and the magnitude of Or is 11.6°, the cone direction is0.5*|21.3°−11.6°|, or 4.9°. For the same reasons discussed above withrespect to the average full cone angle, it can be desirable to determinethe average cone direction of a tip. The average cone direction isdetermined by measuring the cone direction for eight different sideviews of tip 300 (each corresponding to a successive rotation of tip 300about axis 308 by 45° with respect to the previous view), and thencalculating the average of the eight cone direction measurements,resulting in the average cone direction. In some embodiments, theaverage cone direction of tip 300 can be 10° or less (e.g., 9° or less,8° or less, 7° or less, 6° or less, 5° or less), and/or the average conedirection of tip 300 can be 0° or more (e.g., 1° or more, 2° or more, 3°or more, 4° or more). In certain embodiments, the average cone directionof tip 300 is from 0° to 10° (e.g., from 1° to 10°, from 3° to 10°, from6° to 10°, from 2° to 8°, from 4° to 6°).

Tip 300 can also be characterized by its radius of curvature, which canbe determined as follows. FIG. 9 shows a schematic side view of tip 300.In practice, this side view is obtained using a SEM. On either side oflongitudinal axis 308, the slope of the profile of tip 300 is measured.Points 324 and 326 are points on the surface of tip 300 nearest to apex310 where the slope of the profile of tip 300 (indicated by tangentlines 328 and 330, respectively) has a value of 1 and −1, respectively(e.g., 45° lines of inclination). The distance, measured perpendicularto axis 308 and in the plane of FIG. 9, between point 324 and axis 308is the left tangent distance, T_(l), of tip 300. The distance, measuredperpendicular to axis 308 and in the plane of FIG. 9, between point 326and axis 308 is the right tangent distance, T_(r), of tip 300. The leftradius, R_(l), is calculated as R_(l)=√{square root over (2)}·T_(l), andthe right radius, R_(r), is calculated as R_(r)=√{square root over(2)}·T_(r). The radius of curvature, R, of tip 300 is calculated as anaverage of R_(l) and R_(r). Thus, for example, in an embodiment whereT_(l) is 120 nm and T_(r) is 43 nm, R_(l) is 169 nm, R_(r) is 61 nm, andR is 115 nm. For the same reasons as discussed above with respect toaverage full cone angle and average cone direction, it can be desirableto determine the average radius of curvature of a tip. The averageradius of curvature is determined by measuring the radius of curvaturefor eight different side views of tip 300 (each corresponding to asuccessive rotation of tip 300 about axis 308 by 45° with respect to theprevious side view), and then calculating the average of the eight radiiof curvature, resulting in the average radius of curvature. Withoutwishing to be bound by theory, it is believed that if the average radiusof curvature is too small, arcing may occur during tip use and/orionization of He gas may occur in the vicinity of tip atoms other thanthose on the tip's terminal atomic shelf. If the average radius ofcurvature is too large, the ability to reproducibly re-build the tip canbe reduced, and the rate of ionization of He atoms in the vicinity oftip 300 may be reduced due to lower field strengths in the vicinity oftip 300. In some embodiments, the average radius of curvature of tip 300is 200 nm or less (e.g., 180 nm or less, 170 nm or less, 160 nm or less,150 nm or less, 140 nm or less, 130 nm or less), and/or the averageradius of curvature of tip 300 is 40 nm or more (e.g., 50 nm or more, 60nm or more, 70 nm or more, 80 nm or more, 90 nm or more, 100 nm or more,110 nm or more). For example, in some embodiments, the average radius ofcurvature of tip 300 is from 40 nm to 200 nm (e.g., from 50 nm to 190nm, from 60 nm to 180 nm, from 70 nm to 170 nm, from 80 nm to 160 nm).In certain embodiments, the standard deviation of the eight radius ofcurvature measurements is 40% or less (e.g., 30% or less, 20% or less,10% or less) of the average radius of curvature.

FIG. 10 is a flow chart for a process 400 of making a W(111) tip havinga terminal atomic shelf that is a trimer. In a first step 402, a singlecrystal W(111) precursor wire is attached to a support assembly.Typically, the W(111) precursor wire has a diameter of 3 mm or less(e.g., 2 mm or less, 1 mm or less), and/or 0.2 mm or more (e.g., 0.3 mmor more, 0.5 mm or more). In some embodiments, the W(111) precursor wirehas a diameter of from 0.2 mm to 0.5 mm (e.g., from 0.3 mm to 0.4 mm,0.25 mm). Suitable precursor wires can be obtained, for example, fromFEI Beam Technology (Hillsboro, Oreg.).

More generally, in some embodiments, the tip precursor can be in a formthat is different from a wire. For example, the tip precursor can beformed of an electrically conductive material that has a protrusion thatterminates in a crystalline structure. The terminus of the protrusioncan be a single crystal structure, for example, and can be formed ofW(111), or formed of another material in a similar or different crystalorientation.

FIGS. 11A and 11B show perspective and bottom views, respectively, of anembodiment of a support assembly 520. Support assembly 520 includessupport posts 522 a and 522 b connected to a support base 524. Posts 522a and 522 b are connected to heater wires 526 a and 526 b, and a lengthof a W(111) precursor wire 528 is connected to heater wires 526 a and526 b (e.g., via welding). Posts 522 a and 522 b can be connected toauxiliary devices such as, for example, electric current sources (e.g.,power supplies) to permit control of the temperature of W(111) precursorwire 528.

Base 524 provides mechanical support for assembly 520 and is generallyformed of one or more materials that can withstand temperature cycling,and that act as electrical insulators. For example, in some embodiments,base 524 is formed from electrically insulating materials such as glassand/or rigid polymers and/or ceramic.

Posts 522 a and 522 b are generally formed of one or more electricallyconducting materials. Typically, the material used to form posts 522 aand 522 b is chosen so that posts 522 a and 522 b and base 524 have asimilar coefficient of thermal expansion, and so that posts 522 a and522 b remain fixed in position relative to base 524 during temperaturecycling of precursor wire 528. In some embodiments, posts 522 a and 522b are formed from an alloy that includes iron, nickel and cobalt. Anexample of a commercially available material from which posts 522 a and522 b can be formed is KOVAR™.

In general, heater wires 526 a and 526 b are formed from one or morematerials that have higher electrical resistivity than precursor wire528. For example, in some embodiments, heater wires 526 a and 526 b canbe formed from materials such as a tungsten-rhenium alloy. As explainedbelow, heater wires 526 a and 526 b generate heat when electric current(e.g., from an external power supply) is passed through the wires, andthe heat can be used to increase and/or control the temperature ofprecursor wire 528 during various tip processing steps. In general, thediameter and materials of heater wires 526 a and 526 b are selected toensure that suitable control over the temperature of precursor wire 528can be achieved during fabrication processes. In some embodiments,heater wires 526 a and 526 b have diameters of from 100 μm to 750 μm,for example.

The geometrical properties of base 524, posts 522 a and 522 b, andheater wires 526 a and 526 b can generally be selected as desired. Forexample, in some embodiments, a distance between posts 522 a and 522 bcan be from 1 mm to 10 mm.

Optionally, more than two posts (e.g., three posts, four posts, fiveposts, six posts) can be attached to base 524, with each post beingconnected to precursor wire 528 through a corresponding heater wire.Providing additional posts may increase the stability of assembly 520and/or reduce susceptibility of assembly 520 to mechanical vibrations.

In some embodiments, precursor wire 528 can be held in position by asupport assembly that applies a compressive force to the wire. Forexample, FIG. 12 shows an exemplary support assembly 550 including aVogel mount to secure precursor wire 528. Suitable Vogel mounts areavailable commercially from AP Tech (McMinnville, Oreg.), for example.Support assembly 550 includes a support base 556 and mounting arms 552attached to base 556. To secure precursor wire 528, arms 552 are priedapart and spacers (e.g., formed of pyrolytic carbon) 554 are insertedinto the space between the arms. Precursor wire 528 is then insertedinto the opening between spacers 554, and then mounting arms 552 arereleased. Due to the resiliency of arms 552, the arms apply acompressive force to spacers 554 and precursor wire 528 in directionsindicated by arrows 558 and 560, thereby securing precursor wire 528against spacers 554. Static frictional forces between wire 528, spacers554, and arms 552 discourage relative movement of these components,ensuring that wire 528 remains fixed in position in support assembly550. Typically, wire 528 extends above arms 552 a distance of between 1mm and 5 mm, for example.

Base 556 can be formed from materials similar to those which can be usedto form base 524 (e.g., glass and/or rigid polymers and/or ceramic). Thematerial of base 556 is typically an electrically insulating materialthat can withstand temperature cycling.

Mounting arms 552 can be formed from one or more electrically conductingmaterials. The materials used to form arms 552 can also be chosen sothat base 556 and arms 552 have a similar coefficient of thermalexpansion, and so that arms 552 remain fixed in position relative tobase 556 during temperature cycling of precursor wire 528. In someembodiments, arms 552 are formed from an alloy that includes iron,nickel, and cobalt. Suitable commercially available materials forforming arms 552 include KOVAR™.

Spacers 554 are formed from a material such as pyrolytic carbon.Suitable pyrolytic carbon spacers are available from, for example, APTech (McMinnville, Oreg.). Pyrolytic carbon spacers typically are formedof a series of flat carbon sheets stacked atop one another to create alaminar structure. In general, the resistivity of pyrolytic carbonvaries according to direction, with the resistivity of the carbon in adirection perpendicular to the sheets (e.g., in a directionapproximately normal to the planes of the stacked sheets) being higherthan the resistivity along a direction in a plane parallel to the planesof the sheets. During mounting, spacers 554 are oriented so that thehigher resistivity direction of spacers 554 is approximately parallel tothe direction of compressive force applied by arms 552 (e.g.,approximately parallel to arrows 558 and 560). When current isintroduced into arms 552, spacers 554 generate heat due to their highresistivity. Accordingly, spacers 554 can serve as heating elements foradjusting the temperature of precursor wire 528.

Referring again to FIG. 10, in a second step 404, precursor wire 528 isetched in an electrochemical bath to shape the tip of wire 528. Ingeneral, step 404 includes multiple sub-steps.

The first sub-step in the etching process can optionally be a cleaningstep to remove surface contaminants from wire 528. This etching processcan involve disposing wire 528 in an electrochemical etch solution andexposing wire 528 to an alternating current (AC) voltage. For example,the solution can be a 1N solution of sodium hydroxide (NaOH), and an ACvoltage of 1 V can be used. Subsequently, the entire support assembly(e.g., support assembly 520 or 550) can be cleaned (e.g., ultrasonicallycleaned in water) to remove certain remaining contaminants.

The next sub-step in step 404 is to optionally apply a resist materialto a portion of wire 528. Typically, the resist material is applied overa length of approximately 0.5 mm of wire 528, starting from the apex ofwire 528. Application of the resist material can be achieved, forexample, by placing a drop of resist solution onto a clean surface anddipping wire 528 into the resist several times, allowing the resist todry slightly between applications. The applied resist limits the amountof precursor wire 528 that is etched during subsequent processing steps.Because formation of a subsequent tip on a precursor wire 528 oftenfollows removal of a previous tip by etching, use of the resist materialpermits a larger number of tips to be formed on a given precursor wirebefore the wire is discarded. A variety of different resist materialscan be applied to precursor wire 528. An exemplary resist material iscosmetic nail polish. In some embodiments, more than one resist materialmay be used. Use of a resist material is optional to the tip formationprocess, however, and in some embodiments, resist material may not beapplied to precursor wire 528 before undertaking subsequent steps in thefabrication process.

The next sub-step in step 404 is to electrochemically etch precursorwire 528. A variety of electrochemical etching procedures can be used.In some embodiments, the following electrochemical etching procedure isused. The support assembly is placed in an etching fixture that includesa translation apparatus for translating the support assembly, a dish,and an electrode (e.g., a stainless steel electrode) that extends intothe dish. An etching solution is placed in the dish such that thesolution is in contact with the electrode. The support assembly islowered toward the dish via the translation apparatus until the resistinterface on wire 528 just contacts the etching solution. Wire 528 isthen lowered an additional amount (e.g., 0.2 mm) into the etchingsolution.

The etching solution includes a constituent (e.g., NaOH) that chemicallycorrodes wire 528. In embodiments in which the etching solution containsNaOH, the concentration of NaOH in the etching solution can be selectedto vary the corrosion rate of precursor wire 528 and the chemicalenvironment of the solution. For example, in some embodiments, theconcentration of NaOH can be 0.1 M or more (e.g., 0.2 M or more, 0.5 Mor more, 0.6 M or more, 0.8 M or more, 1.0 M or more, 1.2 M or more, 1.4M or more, 1.6 M or more, 2.0 M or more, 2.5 M or more, 3.0 M or more),and/or 10.0 M or less (e.g., 9.0 M or less, 8.0 M or less, 7.0 M orless, 6.5 M or less, 6.0 M or less, 5.5 M or less, 5.0 M or less, 4.5 Mor less, 4.0 M or less). In some embodiments, the concentration of NaOHis from 0.5 M to 10.0 M (e.g., from 1.0 M to 9.0 M, from 1.5 M to 8.0 M,from 2.0 M to 7.0 M, from 2.0 M to 6.0 M, from 2.0 M to 3.0 M).

In certain embodiments, other corrosive agents can be added to theetching solution in place of, or in addition to, NaOH. Examples of suchcorrosive agents include KOH (including molten KOH), HCl, H₃PO₄, H₂SO₄,KCN, and/or molten NaNO₃. Corrosive agents in the etching solution maybe selected based on their ability to corrode a precursor wire formed ofa specific type of material. For example, an agent such as NaOH can beused to corrode wires formed of W. For wires formed of a differentmaterial such as Ir, other corrosive agents can be used in the etchingsolution.

In some embodiments, the etching solution can include a relatively smallamount of surfactant. Without wishing to be bound by theory, it isbelieved that the surfactant can assist in promoting symmetric etchingof precursor wire 528. Suitable surfactants for this purpose includematerials such as PhotoFlo 200, available from Eastman Kodak (Rochester,N.Y.). In general the concentration of surfactant in the etchingsolution is 0.1 volume % or more (e.g., 0.2 volume % or more, 0.3 volume% or more, 0.4 volume % or more), and/or 2 volume % or less (e.g., 1volume % or less, 0.8 volume % or less, 0.6 volume % or less).

In some embodiments, the etching process can also be performed withstirring of the etching solution. The rate at which the etching solutionis stirred can be determined empirically based upon the results of theetching process.

After positioning precursor wire 528 in the etching solution, anexternal power supply is connected to both wire 528 and the electrode,and a potential is applied across wire 528 and the electrode tofacilitate an electrochemical corrosion reaction of wire 528. Ingeneral, the voltage can be applied from either an AC source or a directcurrent (DC) source. The amplitude of the applied voltage can generallybe selected as desired, based upon an empirical determination of anamplitude that produces a uniformly etched precursor wire 528. Forexample, in some embodiments, the amplitude of the applied potential is3.0 V or more (e.g., 3.2 V or more, 3.5 V or more, 4.0 V or more, 5.0 Vor more, 10 V or more, 15 V or more, 20 V or more), and/or 50 V or less(e.g., 40 V or less, 35 V or less, 30 V or less, 25 V or less). In someembodiments, the amplitude of the applied potential is between 3.0 V and50 V (e.g., from 3.5 V to 40 V, from 4.0 V to 30 V, from 4.5 V to 20 V).

The duration of AC pulses applied to the etching solution can generallyvary as desired to promote controlled etching of wire 528. For example,in some embodiments, pulses applied to the etching solution have aduration of 10 ms or more (e.g., 25 ms or more, 50 ms or more, 75 ms ormore, 100 ms or more, 150 ms or more, 200 ms or more, 250 ms or more),and/or one second or less (e.g., 900 ms or less, 800 ms or less, 700 msor less, 650 ms or less, 600 ms or less). In some embodiments, pulsesapplied to the etching solution have a duration of from 10 ms to onesecond (e.g., from 10 ms to 900 ms, from 10 ms to 800 ms, from 10 ms to700 ms, from 10 ms to 600 ms).

In general, pulses of varying duration and/or amplitude can be appliedto the etching solution to cause erosion of precursor wire 528 in theregion of the wire that contacts the solution. Typically, duringprocessing, a portion of the end of precursor wire 528 drops off intothe etching solution, and the newly exposed, etched region of precursorwire 528 is processed further in subsequent steps. For example, asuitable etching regimen includes an initial application ofapproximately 100 AC pulses of amplitude 5 V, each pulse having aduration of approximately 580 ms. Thereafter, a series of approximately60 pulses are applied, with each pulse having a duration ofapproximately 325 ms and an amplitude of 5 V. Then, pulses having aduration of 35 ms and an amplitude of 5 V are applied until a portion ofthe end of wire 528 drops off into the etching solution.

During application of electrical pulses to the etching solution, theimmersion depth of precursor wire 528 can be adjusted. Typically, theetching process leads to formation of a narrow-diameter region ofprecursor wire 528. Adjusting the immersion depth of wire 528 can helpensure that the meniscus of the etching solution is positioned near amid-point of the narrow-diameter region, which can enhance theprobability of forming a relatively symmetric tip. As the drop-off pointis approached (e.g., as the diameter in the narrow-diameter regionbecomes very small), adjustment of the immersion depth is performed toensure that the end of precursor wire 528 is not snapped off. Afterdrop-off of the end of precursor wire 528, the newly exposed tip of wire528 is immersed very slightly in the etching solution and additionalelectrical pulses are applied. In some embodiments, two electricalpulses are applied. As an example, the first pulse can be from 1 V to 10V (e.g., from 3 V to 7V, 5V) with a duration of from 20 ms to 50 ms(e.g., from 30 ms to 40 ms, 35 ms), and the second pulse can be from 1 Vto 10 V (e.g., from 3 V to 7V, 5V) with a duration of from 10 ms to 25ms (e.g., from 15 ms to 20 ms, 17 ms).

The support assembly is then removed from the etching fixture, rinsed(e.g., with distilled or deionized water) and dried (e.g., under astream of dry nitrogen gas).

The next step 406 of process 400 is to examine the support assembly (andparticularly, the etched tip of wire 528) to verify that the etched tiphas suitable geometrical features. As discussed previously, for example,determination of geometrical features includes obtaining profile imagesof the etched tip and calculating various geometrical parameters fromdata obtained from the profile images. The inspection can be performedusing a SEM, for example. Profile images of the tip of wire 528 can beobtained at very high magnification, such as a magnification of 65,000×,for example. The measured geometrical parameters can include average tipradius of curvature, average cone direction, and average full coneangle, for example. At this point, if the shape of the etched tip isunsuitable, it may be possible to re-shape the tip slightly by insertingthe assembly back into the etching fixture and lowering the etched tipof wire 528 toward the dish until the tip just contacts the etchingsolution. A small number of electrical pulses (e.g., from one to threepulses of duration 35 ms and amplitude 5 V) can be used to re-shape thetip of wire 528. For example, if the average full cone angle of the tipof wire 528 is too small, a small number of short duration pulses can beused to increase the average full cone angle without substantiallyincreasing the average radius of the etched tip. Following applicationof these additional electrical pulses, the tip can then be re-examinedin the SEM to verify that it has been correctly re-shaped.

Subsequently, in step 408, the terminal shelf of the apex of the tip ofetched wire 528 is formed into a trimer. This process generally involvesimaging the tip (e.g., using FIM or SFIM) and shaping the tip (e.g.,using field evaporation).

In some embodiments, step 408 includes installing the support assemblyin a FIM and evacuating the FIM. The tip of wire 528 is cooled (e.g., toliquid nitrogen temperature), and He gas is supplied to the FIM (e.g.,at a pressure of approximately 5×10⁻⁶ Torr). A positive potential withrespect to the extractor (e.g., 5 kV or more relative to the extractor)is applied to the tip of wire 528, and the He atoms interact with theapex of the tip of wire 528 to form He ions. The He ions are acceleratedaway from the positively charged apex of the tip of wire 528. Adetector, such as a phosphor screen optically coupled to atwo-dimensional imaging device such as a CCD camera, is positioned at aselected distance from the ion source, and oriented approximatelyperpendicular to the principal ion beam trajectory from the ion source.Impinging ions cause the phosphor screen to emit photons, which aredetected by the CCD camera. Regions of the images that correspond torelatively larger numbers of detected ions will appear brighter thanregions that correspond to relatively fewer numbers of detected ions.Ionization of He gas atoms occurs in the vicinity of individual ionsource atoms at the apex of the tip of wire 528. As a result, imagescaptured by the detector correspond to the emission pattern of the ionsource. More particularly, bright spots in images obtained from thedetector correspond to individual atoms at the ion source apex. Thus,the FIM image is an image of the apex of the tip of wire 528 that isatomically resolved. Based on the FIM image, the crystal structure,orientation, and specific arrangement of atoms at the ion source apexcan be determined.

If the desired properties of the apex of the tip of wire 528 are notpresent, the tip can be shaped, using, for example, field evaporation.During field evaporation, with an image of the etched tip of wire 528 infocus on the FIM detector and with the background pressure of He gasstill present in the FIM, the positive electrical potential on the tipis increased (e.g., 15 kV or more relative to the extractor) until theresulting field begins to remove W atoms (and contaminant atoms) frompositions on the tip where the local electric field is highest. The rateat which atoms are removed is controlled to prevent groups of atoms frombeing removed simultaneously. In general, field evaporation continueswith monitoring of the FIM emission pattern until it is verified thatthe surface of the etched tip is in the correct crystal orientation, andit is determined that there are no undesirable contaminants at theterminal shelf of the tip.

After field evaporation, it may be desirable to sharpen the tip. Tosharpen the tip, the He gas is pumped out of the FIM chamber, and thebias on the tip of wire 528 is changed to being negative with respect tothe common ground so that the apex of the tip of wire 528 emitselectrons. A detector which generates photons in response to incidentelectrons, such as a phosphor-coated glass screen, is positioned tointercept electrons from the tip. The generated photons are detected bya suitable detector (e.g., a CCD device, a photomultiplier tube, aphotodiode, or another type of photon detector) and used to monitorelectron emission from the tip. In some embodiments, the detector can bedirectly coupled to the photon-generating device. In certainembodiments, the detector and photon-generating device are not directlycoupled. For example, optical elements such as mirrors can be used todirect generated photons to the detector.

The voltage bias applied to the tip is adjusted until a desired electroncurrent is measured (e.g., from 25 pA to 75 pA, from 40 pA to 60 pA, 50pA). The tip is then heated to a desired temperature (e.g., from 1000 Kto 1700 K, from 1300 K to 1600 K, 1500 K), and the tip is monitoredvisually to detect light emitted from the tip in response to theapplication of both voltage and heat. Light emission from the tip can bemonitored, for example, using a mirror positioned to reflect lightemitted by the tip toward a suitable photon detector (e.g., a CCDdevice, a photomultiplier tube, a photodiode, or another type of photondetector). Heat can be applied to the tip using a variety of devicessuch as a resistive heating device (e.g., a filament heater), aradiative heating device, an inductive heating device, or an electronbeam. From 15 seconds to 45 seconds (e.g., from 25 seconds to 35seconds, 30 seconds) after the first appearance of light from the tip,both the applied potential and the heating device are turned off,yielding wire 528 with a trimer as its terminal atomic shelf.

Optionally, a gas can be used to sharpen the tip. For example, oxygencan be introduced into the FIM chamber to promote sharpening of arounded W tip surface. The sharpening gas (e.g., oxygen) is introducedafter He has been removed from the FIM chamber, and the tip is heated inthe presence of oxygen at a selected pressure for a period of time. Forexample, to sharpen a rounded W tip, He is first pumped out of the FIMchamber and then the tip is heated to a temperature of between 1300 Kand 1700 K (e.g., 1500 K). The tip is maintained at 1500 K for betweenone and five minutes. Next, oxygen can be introduced into the chamber ata pressure of approximately 10⁻⁵ Torr, while maintaining the temperatureof the tip for approximately two minutes. With oxygen flow to thechamber continuing, the temperature of the tip is then reduced tobetween 700 K and 1200 K (e.g., 1000 K), and the tip is maintained atthat temperature for approximately two minutes. Finally, the oxygensupply to the chamber is closed and oxygen is pumped out of the chamberuntil the oxygen pressure therein is less than 10⁻⁷ Torr. At the sametime, the tip is cooled to its normal operating temperature (e.g.,approximately 77 K in some embodiments) and He is re-introduced into theFIM chamber. When the tip is imaged in FIM mode, a W trimer atop the tipcorresponding to a W(111) facet is observed. The W(111) wire having aterminal shelf that is a trimer can then be removed from the FIM andstored for future use.

Although the foregoing describes embodiments in which a FIM separatefrom system 200 is used to image/shape the wire tip apex, in someembodiments, system 200 can be used as the FIM. In such embodiments, thesupport assembly is installed within the ion source and system 200 isoperated as a FIM, generally according to the procedure described in thepreceding paragraphs. In some embodiments, when operating system 200 inFIM mode, the detector can be positioned either where sample 280 isnormally positioned (i.e., sample 180 is not present in its normalposition). In certain embodiments, when operating system 200 in FIMmode, a flat sample with a relatively high secondary electron yield canbe positioned where sample 180 is normally positioned, and the secondaryelectrons generated by the interaction of the He ions with the flatsample are detected because the intensity of the secondary electronsdetected will generally scale with the intensity of the He ions incidenton the flat sample.

Optionally, system 200 can be operated in SFIM mode during the processof imaging/shaping the wire tip apex. In such embodiments, the processis as described in the preceding paragraphs, except that alignmentdeflectors 220 and 222 are used to raster the ion beam across thesurface of aperture 224 to generate a field emission pattern of the apexof the wire tip. Portions of the ion beam which pass through aperture224 can optionally be focused by second lens 226, or remain unfocused.In SFIM mode, an image of the wire tip is acquired pixel-by-pixel, andeach measured pixel intensity corresponds to a portion of ion beampermitted to pass through aperture 224. The pixel intensities togethercan be used to represent the field emission pattern of the tip as animage or, more generally, as a plurality of electrical signals. Thefield emission pattern can then be used to assess various properties ofthe tip to determine its suitability for use in a gas field ionmicroscope. In SFIM mode, the detector can be located and of the type asdescribed in the preceding paragraphs. Optionally, the detector can be aspatially integrating detector such as a photomultiplier tube or aphotodiode.

The procedures described above can generally be used to sharpen a W tipfor the first time, and can also be used for re-sharpening of a W tipwithin an ion microscope system. Such re-sharpening can be performed insystem 200 even if the initial process for sharpening the W tip wasperformed in a FIM other than system 200. Re-sharpening can generally beperformed in the same manner as the initial sharpening, or there-sharpening techniques can be different from the original sharpeningtechnique. In some embodiments, to assess whether re-sharpening isdesirable, microscope system 200 can be configured to operate in FIMand/or SFIM mode, as described above. Based upon one or more images ofthe tip, the re-sharpening process can be initiated or postponed. Incertain embodiments, other criteria can be used to determined when toinitiate re-sharpening. For example, if the measured ion current fromthe tip falls below an established threshold value after a period ofoperation, re-sharpening can be initiated.

As a first step in re-sharpening, the tip can be field evaporated toremove atoms near the tip apex. For example, microscope system 200 canbe configured to operate in FIM and/or SFIM mode, as discussed above,and the potential applied to the tip can be carefully adjusted toproduce controlled field evaporation of tip atoms. During the fieldevaporation process, a field emission image of the tip can be obtainedin FIM or SFIM mode by a detector (e.g., a phosphor-coupled photondetector, or a secondary electron detector configured to measuredsecondary electron emission from a flat sample) and monitored todetermine when to halt the field evaporation process. As before, whenthe surface of the tip is in the correct crystal orientation and isclean, the tip can be re-sharpened.

He gas is pumped out of microscope system 200 until the background Hepressure is less than approximately 10⁻⁷ Torr. In some embodiments, toinitiate re-sharpening, a negative electrical potential is applied tothe tip to operate microscope system 200 in electron mode, and the tipis sharpened via heating as described previously. In certainembodiments, a sharpening gas such as oxygen is introduced intomicroscope system 200, and the tip is heated in the presence of oxygenfor a selected time, as described previously. Following there-sharpening procedure, He gas is re-introduced into microscope system200, and with the system configured to operated in FIM and/or SFIM mode,one or more images of the re-sharpened tip are captured to verify thatthe tip apex includes a trimer corresponding to a W(111) facet.

In some embodiments, certain re-sharpening steps can be performedautomatically by hardware and/or software in electronic control system170. For example, in certain embodiments, the sharpening procedure thatis applied to a rounded tip can be performed in an automated manner. Anexample of a sharpening algorithm implemented by electronic controlsystem 170 is as follows. First, control system 170 evacuates microscopesystem 200 by activating pumps 236 and/or 237 and cools the tip toliquid nitrogen temperature. When the background pressure of gas inmicroscope system 200 is less than an established threshold, the tip isheated by control system 170 to a temperature of 1500 K by applying acalibrated electrical current to the heater wires supporting the tip.After two minutes at 1500 K, control system 170 introduces oxygen gasinto microscope system 200 by opening a valve on an oxygen gas source.The valve opening is adjusted to maintain an oxygen pressure ofapproximately 10⁻⁵ Torr in microscope system 200. After two additionalminutes, the temperature of the tip is reduced to 1100 K by controlsystem 170 by regulating the flow of liquid nitrogen coolant into thesystem. After two minutes at 1100 K, control system 170 shuts off theoxygen supply to the system and cools the tip to liquid nitrogentemperature. At this point, FIM and/or SFIM images of the tip (measuredby an operator) can be used to manually verify the presence of a W(111)at the apex of the tip.

Without wishing to be bound by theory, it is believed that oxygen canpromote formation of a trimer as the terminal atomic shelf of a tip. Incertain embodiments, the pressure of oxygen gas in the FIM chamber canbe 10⁻⁷ Torr or more (e.g., 10⁻⁶ Torr or more, 10⁻⁵ Torr or more, 10⁻⁴Torr or more), and/or 1 Torr or less (e.g., 10⁻¹ Torr or less, 10⁻² Torror less, 10⁻³ Torr or less). In certain embodiments, the pressure ofoxygen gas in the FIM chamber can be from 10⁻⁸ Torr to 10⁻² Torr (e.g.,from 10⁻⁷ Torr to 10⁻³ Torr, from 10⁻⁶ Torr to 10⁻⁴ Torr). Other gasesand materials can also be used to promote formation of a trimer as theterminal atomic shelf during tip sharpening. For example, materials suchas palladium, platinum, gold, and/or iridium can be vapor deposited ontothe surface of a rounded tip prior to re-sharpening. It is believed thatthese materials may promote more reliable trimer formation at the apexof the tip.

In some embodiments, sharpening of a W tip can be achieved by controlledheating of the tip without the application of a field or the intentionaladdition of oxygen. For example, a W tip can be sharpened by thefollowing steps: 1) install tip in FIM chamber; 2) reduce pressure inFIM chamber; 3) heat tip to 1000 K for five minutes; and cool (e.g., toliquid nitrogen temperature). Without wishing to be bound by theory, itis believed that trace amounts of oxygen present on the tip as oxidesmay assist in sharpening the tip using heat. In certain embodiments, anunsharpened tip can be exposed to a stream of oxygen, placed in asubstantially oxygen-free environment, and sharpened by controlledheating. It is believed that this approach may produce W oxides on thesurface of the tip, and oxygen liberated from the W oxides upon heatingmay assist the tip sharpening process.

In some embodiments, one or more additional gases may be present duringtip sharpening. For example, in certain embodiments, nitrogen gas may bepresent. Without wishing to be bound by theory, it is believed thatnitrogen gas may assist in etching the tip to provide a more roundedstructure with a terminal atomic shelf that is a trimer; such astructure is believed to be more stable than a less-rounded,trimer-terminated tip. In general, the nitrogen gas is introducedsimultaneously with the oxygen gas. In certain embodiments, the pressureof nitrogen gas in the FIM chamber can be 10⁻⁸ Torr or more (e.g., 10⁻⁷Torr or more), and/or 10⁻⁵ Torr or less (e.g., 10⁻⁶ Torr). In certainembodiments, the pressure of nitrogen gas in the FIM chamber can be from10⁻⁵ Torr to 10⁻⁸ Torr (e.g., from 10⁻⁶ Torr to 10 ⁻⁷ Torr).

Optionally, after forming the trimer and to assist in ensuring that thetip sharpening process is repeatable, the positive electrical potentialapplied to the sharpened tip is increased so that controlled fieldevaporation of the tip occurs. After field-evaporating the tip for aperiod of time, the tip apex reassumes a rounded shape. Typically, therounded tip produces an emission pattern that is similar to the emissionpattern of the tip after the initial field evaporation step. Then, therounded tip is again sharpened in electron mode to produce a terminalatomic shelf that is a trimer (e.g., using the procedure describedabove). In some embodiments, to increase the sharpened tip lifetime andstability, one or more trimers can be removed from the sharpened tipusing field evaporation techniques. For example, the top-most atomiclayer on the sharpened tip, which is formed by a three-atom shelf, canbe removed to reveal an atomic shelf underneath that includes more thanthree atoms. The newly exposed atomic shelf can be further fieldevaporated to produce a W atom trimer at its apex. This newly formedtrimer, along with additional trimers formed during field evaporation,can be evaporated. This process leads to a layer-by-layer rounding ofthe tip in the vicinity of its apex. By rounding the tip, the electricfield gradient near the tip apex is reduced, reducing the probabilitythat tip atoms undergo field evaporation while microscope system 200 isoperating, and increasing the stability and lifetime of the tip.

In step 410 of process 400, the apex 187 of tip 186 is aligned withinsystem 200. With the support assembly installed in microscope system200, microscope system 200 is evacuated using one or more vacuum pumps,and then heat is applied to tip 187 to remove, for example, oxides,condensates, and/or any other impurities that may have adhered to thetip surface. Typically, for example, tip 186 is heated to a temperatureof 900 K or more (e.g., 1000 K or more, 1100 K or more) for a durationof 10 s or more (e.g., 30 s or more, 60 s or more). Heating may alsoassist in re-faceting tip 186, in the event that the tip shape iscompromised by the presence of impurities.

With tip 186 glowing radiatively as a result of the applied heat, thetip is then roughly aligned with the longitudinal axis of ion optics 130by observing light from tip 186 propagating along the longitudinal axis(e.g., by inserting a reflective element such as a mirror and directinga portion of the light to a detector such as a CCD camera). The positionand/or orientation of tip 186 can be changed by adjusting tipmanipulator 208 to direct the light from tip 186 through ion optics 130.

Following this rough alignment procedure, microscope system 200 isconfigured to operate in FIM or SFIM mode by reducing the backgroundpressure in vacuum housings 202 and 204, cooling tip 186 (e.g., toapproximately liquid nitrogen temperature), and introducing a stream ofHe gas atoms into a region in the vicinity of tip 186 via gas source110. An image of the field emission pattern of He ions from tip 186 ismeasured by a suitably configured detector and based upon this image,tip manipulator 208 is used to align the field emission pattern with alongitudinal axis of ion optics 130, so that the field emission patternof tip 186 is centered upon the longitudinal axis. A centering test canbe performed by changing the electrical potential applied to first lens216 while observing the induced modulation of the field emission patternof tip 186. If the size of the field emission pattern observed by thedetector changes due to the variation of the electrical potentialapplied to lens 216, but the position of the center of the pattern doesnot change, then tip 186 is aligned with a longitudinal axis of firstlens 216. Conversely, if the center position of the field emissionpattern of tip 186 changes in response to the variation of the potentialapplied to first lens 216, then tip 186 is not centered on thelongitudinal axis of first lens 216. Adjustments of the orientation andposition of tip 186 via tip manipulator 208 can be repeated iterativelyuntil tip 186 is sufficiently well aligned with the longitudinal axis offirst lens 216. Typically, this centering test is performed withoutaperture 224 in position.

A fine alignment procedure can then be performed to ensure that He ionsgenerated via the interaction of He gas atoms with the three-atom shelfat apex 187 of tip 186 pass through aperture 224. The electricalpotentials applied to deflectors 220 and 222 (see discussion below) areadjusted so that 70% or more (e.g., 75% or more, 80% or more, 85% ormore, 90% or more, 95% or more, 97% or more, 99% or more) of the He ionsin ion beam 192 that pass through aperture 224 are generated via theinteraction of He gas atoms with only one of the three trimer atoms atthe apex of tip 186. At the same time, the adjustment of the potentialsapplied to deflectors 220 and 222 ensures that aperture 224 prevents 50%or more (e.g., 60% or more, 70% or more, 80% or more, 90% or more, 95%or more, 98% or more) of the He ions in ion beam 192 generated by theinteraction of He gas atoms with the other two trimer atoms fromreaching surface 181 of sample 180. As a result of this fine alignmentprocedure, the He ion beam that passes through aperture 224 and exitsion optics 130 includes He atoms that were ionized primarily in thevicinity of only one of the three trimer atoms at the apex of tip 186.

Referring again to FIG. 10, with tip 186 aligned with the longitudinalaxis of first lens 216, and the He ion beam aligned so that a portion ofion beam 192 passes through aperture 224, microscope system 200 can beoperated in He ion mode in step 412 of process 400. In embodiments inwhich system 200 was used in FIM mode during tip sharpening, the FIMdetectors and/or other FIM componentry is moved so that sample 180 canbe positioned for exposure to ion beam 192. An electrical potential thatis positive with respect to extractor 190 is applied to tip 186, and Hegas is introduced into vacuum housing 202 via gas source 110. He ionsgenerated via the interaction of He gas atoms with primarily one of thethree trimer atoms at the apex of tip 186 are guided by ion optics 130through aperture 224, and are directed to sample 180.

In some embodiments, the potential applied to tip 186 is 5 kV or more(e.g., 10 kV or more, 15 kV or more, 20 kV or more). In certainembodiments, the potential applied to tip 186 is 35 kV or less (e.g., 30kV or less, 25 kV or less). For example, in some embodiments, thepotential applied to tip 186 is from 5 kV to 35 kV (e.g., from 10 kV to30 kV, from 15 kV to 25 kV).

In some embodiments, during operation of microscope system 200, the Hegas pressure is 10⁻⁸ Torr or more (e.g., 10⁻⁷ Torr or more, 10⁻⁶ Torr ormore, 10⁻⁵ Torr or more). In certain embodiments, the He gas pressure inmicroscope system 200 is 10⁻¹ Torr or less (e.g., 10⁻² Torr or less,10⁻³ Torr or less, 10⁻⁴ Torr or less). For example, in some embodiments,the He gas pressure in microscope system 200 is from 10⁻⁷ Torr to 10⁻¹Torr (e.g., from 10⁻⁶ Torr to 10⁻² Torr, from 10⁻⁵ Torr to 10⁻³ Torr).

To verify the integrity of tip 186, the field emission pattern from tip186 can be periodically monitored by operating microscope system 200 inFIM or SFIM mode, as discussed above. If the trimer structure remainsintact at tip apex 187, then tip 186 can continue to be used to provideion beam 192 to microscope system 200. However, under certaincircumstances, FIM or SFIM imaging of tip 186 may reveal that the trimerstructure is no longer intact on tip apex 187. In this case, tip 186 canfirst be field evaporated to round the tip and remove the damaged trimerstructure, and then re-sharpened in situ (e.g., without removing tip 186from microscope system 200) using a process as described above.

Monitoring of the field emission pattern from tip 186 can be performedautomatically based on criteria such as reduced performance (e.g.,reduced ion current), observed imaging aberrations and/or errors, orother pre-determined criteria. To capture a FIM image of tip 186, sample180 can be removed from its position and a detector, such as aphosphor-coupled CCD detector, can be placed at the former location ofsample 180. Alternatively, a flat sample with a relatively highsecondary electron yield can be translated into position in place ofsample 180, and a suitable detector can be positioned and configured todetect secondary electrons that leave the sample due to the interactionof the He ions with the sample. Aperture 224 can be removed (or a largediameter opening 225 can be selected) so that ions generated from theinteraction of He gas atoms with tip 186 are not significantlyobstructed. These operations can be performed in an automated fashion.

To capture a SFIM image of tip 186, a detector can be introduced asdescribed for FIM imaging, and aperture 224 can be maintained inposition. Alignment deflectors 220 and 222 can be used to raster the ionemission pattern of tip 186 across aperture 224 to acquire an image oftip 186 in pixel-by-pixel fashion. Acquisition of one or more images oftip 186 can be automated by electronic control system 170, which cancontrol placement of apertures, movement of samples and detectors, andelectrical potentials applied to tip 186 and to alignment deflectors 220and 222.

Referring to FIG. 13, the alignment procedure described above typicallyaligns a longitudinal axis 207 of tip 186 with a longitudinal axis 132of ion optics 130 so that the distance d between axes 207 and 132 atapex 187 of tip 186 is less than 2 mm (e.g., less than 1 mm, less than500 μm, less than 200 μm). In some embodiments, the angle between axes207 and 132 at apex 187 of tip 186 is 2° or less (e.g., 1° or less, 0.5°or less, 0.2° or less).

Extractor 190 includes an opening 191. In general, the shape ofextractor 190 and of opening 191 can be selected as desired. Typically,these features are chosen to ensure that He ions are efficiently andreliably directed into ion optics 130. For example, as shown in FIG. 13,extractor 190 has a thickness t_(e) measured in the z direction, anopening 191 of width a measured in the x-direction, and is positioned adistance e measured in the z-direction from apex 187 of tip 186. In someembodiments, t_(e) is 100 μm or more (e.g., 500 μm or more, 1 mm ormore, 2 mm or more), and/or t_(e) is 10 mm or less (e.g., 7 mm or less,5 mm or less, 3 mm or less). In certain embodiments, the distance ebetween apex 187 of tip 186 and extractor 190 is 10 mm or less (e.g., 8mm or less, 6 mm or less, 5 mm or less, 4 mm or less, 3 mm or less, 2 mmor less, 1 mm or less). In some embodiments, extractor 190 is positionedfurther in the +z direction than tip 186, as shown in FIG. 13. Incertain embodiments, extractor 190 is positioned further in the −zdirection than tip 186. In such embodiments, for example, tip 186protrudes through extractor 190 and extends further along the z-axis inthe +z direction than extractor 190. While extractor 190 is shown ashaving a particular configuration in FIG. 13, more generally, extractor190 can be of any desired design. For example, in some embodiments,opening 191 can have curved sides of any desired shape.

Extractor 190 can generally be biased either positively or negativelywith respect to tip 186. In some embodiments, the electrical potentialapplied to extractor 190 is −10 kV or more (e.g., −5 kV or more, 0 kV ormore), and/or 20 kV or less (e.g., 15 kV or less, 10 kV or less) withrespect to tip 186.

Optionally, suppressor 188 can also be present in the vicinity of tip186. Suppressor 188 can be used, for example, to alter the electricfield distribution in the vicinity of tip 186 by adjusting the potentialapplied to suppressor 188. Together with extractor 190, suppressor 188can be used to control the trajectory of He ions produced at tip 186.Suppressor 188 has an opening of width k measured in the x-direction, athickness t_(s) measured in the z-direction, and is positioned at adistance s, measured in the z-direction, from the apex of tip 186. Insome embodiments, k is three μm or more (e.g., four μm or more, five μmor more) and/or eight μm or less (e.g., seven μm or less, six μm orless). In certain embodiments, t_(s) is 500 μm or more (e.g., 1 mm ormore, 2 mm or more), and/or 15 mm or less (e.g., 10 mm or less, 8 mm orless, 6 mm or less, 5 mm or less, 4 mm or less). In some embodiments, sis 5 mm or less (e.g., 4 mm or less, 3 mm or less, 2 mm or less, 1 mm orless). In certain embodiments, as shown in FIG. 13, suppressor 188 ispositioned further along in the +z-direction than tip 186. In someembodiments, tip 186 is positioned further along in the +z-directionthan suppressor 188, so that tip 186 extends through suppressor 188 inthe +z-direction.

In general, microscope system 200 can be configured so that afterpassing through extractor 190, the energy of the ions in ion beam 192can be selected as desired. Typically, the average energy of the ions inion beam 192 is 5 keV or more (e.g., 10 keV or more, 20 keV or more, 30keV or more) and/or 100 keV or less (e.g., 90 keV or less, 80 keV less,60 keV or less, 50 kV or less, 40 kV or less, 30 kV or less) afterpassing through entry opening 133 to ion optics 130. For example, insome embodiments, after passing through entry opening 133, the energy ofthe ions in ion beam 192 is from 5 keV to 100 keV (e.g., from 10 keV to90 keV, from 20 keV to 80 keV). For example, in embodiments where it isdesirable to detect ions that are transmitted through a sample, higherion energies (e.g., 50 keV to 100 keV) may be used.

Further, in certain embodiments, the energy of the ions in ion beam 192can be changed without changing the ion current. That is, the electricalpotential applied to tip 186 can be adjusted to modify the averageenergy of ion beam 192 without substantially changing the ion beamcurrent from ion beam 192.

C. Ion Optics

Referring to FIG. 14, ion beam 192 enters ion optics 130 via entryopening 133 from gas field ion source 120. Ion beam 192 passes firstthrough first lens 216. The position and electrical potential of firstlens 216 are generally selected to focus ion beam 192 to a cross-overpoint C, where point C is a distance p, measured in the z-direction,from aperture 224. In general, first lens 216 is positioned a distancef, measured in the z-direction, from entry opening 133. In someembodiments, the distance f is 5 mm or more (e.g., 10 mm or more, 15 mmor more), and/or 30 mm or less (e.g., 25 mm or less, 20 mm or less).

In general, first lens 216 can be biased positively or negatively withrespect to tip 186. In some embodiments, the electrical potentialapplied to first lens 216 is −30 kV or more (e.g., −20 kV or more, −10kV or more), and/or 40 kV or less (e.g., 30 kV or less, 20 kV or less,15 kV or less, 10 kV or less) relative to tip 186.

In general, the distance p can be 1 mm or more (e.g., 5 mm or more, 10mm or more), and/or 100 mm or less (e.g., 70 mm or less, 50 mm or less,30 mm or less, 20 mm or less). Changing the position of point C canchange the size of ion beam 192 in the x- and/or y-directions at theposition of aperture 224, which can selectively control the fraction ofions in ion beam 192 that pass through aperture 224. Although shown inFIG. 14 as being positioned further in the −z-direction than aperture224, cross-over point C can, in some embodiments, be positioned furtherin the +z-direction than aperture 224.

Alignment deflectors 220 and 222 are configured to direct a portion ofion beam 192 to pass through both aperture 224 and second lens 226.Various designs and/or components can be used to construct thedeflectors. In some embodiments, for example, deflectors 220 and 222 caneach be quadrupole electrodes, with the two quadrupole electrodes beingarranged in series.

Deflectors 220 and 222 can each deflect He ion beam 192 in both x- andy-directions. The electrical potentials applied to the electrodes ofdeflectors 220 and 222 can be adjusted to ensure that a portion of ionbeam 192 passes through both aperture 224 and second lens 226. Incertain embodiments, the potentials applied to deflectors 220 and 222are adjusted to achieve a particular alignment condition, and then thepotentials remain static while microscope system 200 is in operation.Alignment of ion beam 192 through aperture 224 is assessed by observingion beam 192 using a suitable detector configured, for example, to imageaperture 224. Deflectors 220 and/or 222 can also be adjusted so that theportion of ion beam 192 that passes through aperture 224 is aligned witha longitudinal axis of second lens 226. To assess alignment of ion beam192 through second lens 226, the electrical potential applied to secondlens 226 can be varied (commonly referred to as wobbling) and theresults observed on the imaging detector. If, as a result of thechanging potential applied to second lens 226, the image of ion beam 192changes in size but not in position, then ion beam 192 is alignedthrough second lens 226. If the position of the center of ion beam 192changes as a result of the changing potential, then ion beam 192 is notaligned with second lens 226. In this case, the potentials applied todeflectors 222 and/or 220 can be further adjusted and the wobble testrepeated, in iterative fashion, until alignment is achieved.

In general, electrical potentials applied to various electrode elementsof alignment deflectors 220 and 222 can be selected as desired toproduce deflection of ion beam 192 to a particular location relative toboth aperture 224 and second lens 226. Each of the electrodes indeflectors 220 and 222 can be biased either positively or negativelywith respect to a common external ground. In general, the electricalpotential applied to any electrode can be 100 V or less (e.g., 75 V orless, 50 V or less) and/or 10 V or more (e.g., 25 V or more, 40 V ormore) relative to a common external ground. During operation, forexample, the electrical potential applied to any electrode in deflectors220 and 222 can be from 10 V to 100 V (e.g., from 10 V to 75 V, from 10V to 50 V) relative to a common external ground.

Aperture 224 is positioned relative to ion beam 192 to permit a fractionof the ions in ion beam 192 to pass therethrough. Typically, aperture224 does not have an applied electrical potential. In some embodiments,the width w, measured in the x-direction, of opening 225 in aperture 224is one μm or more (e.g., 2 μm or more, 5 μm or more, 10 μm or more, 15μm or more, 20 μm or more, 25 μm or more, 30 μm or more), and/or 100 μmor less (e.g., 90 μm or less, 80 μm or less, 70 μm or less, 60 μm orless, 50 μm or less). For example, in certain embodiments, w is from oneμm to 100 μm (e.g., from 5 μm to 90 μm, from 15 μm to 50 μm, from 20 μmto 50 μm). In some embodiments, the width of opening 225 in aperture 224measured in the y direction is one μm or more (e.g., 2 μm or more, 5 μmor more, 10 μm or more, 15 μm or more, 20 μm or more, 25 μm or more, 30μm or more), and/or 100 μm or less (e.g., 90 μm or less, 80 μm or less,70 μm or less, 60 μm or less, 50 μm or less). For example, in certainembodiments, w is from one μm to 100 μm (e.g., from 5 μm to 90 μm, from15 μm to 50 μm, from 20 μm to 50 μm).

Aperture 224 is positioned on aperture mount 234. Aperture mount 234permits translation of aperture 224 in the x-y plane, according tocontrol signals received from electronic control system 170. In someembodiments, aperture mount 234 can also permit translation of aperture224 in the z direction along longitudinal axis 132 of ion optics 130.Further, in certain embodiments, aperture mount 234 can permit tiltingof aperture 224 with respect to the x-y plane. Tilting aperture 224 canbe used to align a longitudinal axis of aperture 224 with longitudinalaxis 132 of ion optics 130.

In some embodiments, aperture 224 can include a plurality of openingshaving different widths w. For example, FIG. 15 is a top view (along thez-direction) of a disk-shaped aperture 224 a that includes multipleopenings 225 a-225 g. Aperture 224 a is configured to rotate about apivot point 227 that coincides with the center of aperture 224 a. Thecenters of each of openings 225 a-225 g are positioned at the samedistance from pivot point 227. An aperture opening of a particular sizecan therefore be selected by rotating aperture disk 224 a such that aselected opening is positioned in the path of ion beam 192, and thentranslating aperture disk 224 a, if desired, to ensure correct alignmentof the opening with ion beam 192.

FIG. 16 is a top view (along the z-direction) of a rod-shaped aperture224 b that includes multiple openings 229 a-229 e extending throughaperture 224 b. The aperture size can be chosen by selecting an openingin aperture 224 b. This selection is performed by translating aperture224 b in a direction parallel to arrow 221 to align one of the openings229 a-229 e with ion beam 192.

Typically, openings 225 a-225 g and 229 a-229 e have diameters that canbe chosen as desired. For example, in some embodiments, the diameter ofany of the openings can be five μm or more (e.g., 10 μm or more, 25 μmor more, 50 μm or more) and/or 200 μm or less (e.g., 150 μm or less, 100μm or less). In certain embodiments, the diameters of openings 225 a-225g and/or 229 a-229 e can be from five μm to 200 μm (e.g., five μm to 150μm, five μm to 100 μm).

In some embodiments, devices other than an aperture can be used topermit only a portion of the ions in ion beam 192 to pass through ionoptics 130 and impinge on the surface of sample 180. For example, twoperpendicular slits can be positioned in series along the flight path ofthe ion beam.

Astigmatism corrector 218 is generally configured, via its shape,position along the path of ion beam 192, and applied electricalpotential, to reduce or eliminate astigmatism in ion beam 192. Althoughvarious components can be used to construct astigmatism corrector 218,astigmatism corrector 218 is typically an octupole electrode positionedbetween aperture 224 and scanning deflectors 219 and 221. Typically, theeight electrodes of an octupolar astigmatism corrector are divided intotwo groups of four electrodes, with a first controller configured toadjust the voltages of four of the electrodes (e.g., the first group offour electrodes, positively biased with respect to tip 186) and a secondcontroller that adjusts the voltages of the other four electrodes (e.g.,the second group of four electrodes, negatively biased with respect totip 186). Electrodes from the first and second electrode groups arearranged in alternating fashion to form the segments of the octupole,where adjacent segments have bias voltages of opposite signs. Thisarrangement of electrodes forms a cusp field which focuses ion beamspropagating along a longitudinal axis of the octupole, and de-focusesoff-axis ion beams.

In general, each of the electrodes of the octupole can be configuredindependently, and astigmatism corrector 218 therefore permits sensitivecontrol over ion beam 192. In some embodiments, the electrical potentialapplied to any of the electrodes of astigmatism corrector 218, relativeto the common external ground, can be −30 V or more (e.g., −20 V ormore, −10 V or more, −5 V or more), and/or 30 V or less (e.g., 20 V orless, 10 V or less, 5V or less).

In addition to alignment deflectors 220 and 222, ion optics 130 includescanning deflectors 219 and 221. Scanning deflectors 219 and 221 aretypically positioned between astigmatism corrector 218 and second lens226, although in general, other arrangements of scanning deflectors 219and 221 within ion optics 130 are also possible.

Scanning deflectors 219 and 221 are configured to scan ion beam 192across a surface of sample 180. Deflector 219, for example, can beconfigured to deflect ion beam 192 in the x-direction, and deflector 221can be configured to deflect ion beam 192 in the y-direction. Thecombined deflection produced by deflectors 219 and 221 can position ionbeam 192 at a particular location on sample 180.

Typically, the electrical potentials applied to deflectors 219 and 221are adjusted to produce a particular deflection of ion beam 192. Theapplied electrical potentials can be varied systematically to rasterscan beam 192 over a portion of sample 180. For example, in someembodiments, the electrical potential applied to deflector 221 isincreased in stepwise fashion at regular intervals to deflect ion beam192 across sample 180 in discrete steps (e.g., row-by-row) in they-direction. At the same time, the electrical potential applied todeflector 219 is increased in stepwise fashion to deflect ion beam 192across sample 180 in discrete steps (e.g., column-by-column) in thex-direction. The rate at which the potential applied to deflector 221 isincreased can be selected so that ion beam 192 is deflected in they-direction to a new row once ion beam 192 has made a complete scanacross all columns via the stepwise increases in the potential appliedto deflector 219. For each row, the same stepwise pattern of incrementalpotential increases can be applied to deflector 219 to sweep ion beam192 in discrete steps in the x-direction.

In general, scanning deflectors 219 and/or 221 can be formed from aplurality of electrodes. For example, in some embodiments, scanningdeflectors 219 and/or 221 can each include a pair of parallel plateelectrodes. The electrodes in deflector 219 can be oriented to deflection beam 192 in a direction orthogonal to the deflection of ion beam 192produced by deflector 221.

In certain embodiments, scanning deflectors 219 and/or 221 can be of amore complex design. For example, scanning deflectors 219 and/or 221 caninclude quadrupolar electrodes and/or octupolar electrodes. Theseelectrodes can each be configured to provide deflection of ion beam 192in a single direction in the x-y plane, or in more than one direction inthe x-y plane.

Each of the electrode elements in scanning deflectors 219 and 221 can bebiased either positively or negatively with respect to the commonexternal ground. In general, the voltage applied to each electrode canbe −150 V or more (e.g., −100 V or more, −50 V or more, −20 V or more)and/or 150 V or less (e.g., 100 V or less, 50 V or less, 20 V or less).During operation, for example, the voltage applied to each electrode indeflectors 219 and 221 can be from −150 V to 150 V (e.g., from −100 V to100 V, from −50 V to 50 V, from −20 V to 20 V).

In general, the position and electrical potential of second lens 226 areselected so that second lens 226 assists in focusing ion beam 192 ontosurface 181 of sample 180. The electrical potential applied to secondlens 226 can, in general, be either positive or negative with respect tothe common external ground. In certain embodiments, the electricalpotential applied to second lens 226 is −50 kV or more (e.g., −40 kV ormore, −30 kV or more), and/or 40 kV or less (e.g., 30 kV or less, 20 kVor less) relative to the common external ground. Second lens 226 isspaced from aperture 224 by a distance u, measured in the z direction.In some embodiments, u is 5 cm or more (e.g., 10 cm or more, 15 cm ormore), and/or 50 cm or less (e.g., 45 cm or less, 40 cm or less, 35 cmor less, 30 cm or less, 25 cm or less, 20 cm or less).

Second lens 226 is spaced from sample 180 by a distance h (commonlyreferred to as the working distance) measured along the z-axis. In someembodiments, h can be 2 mm or more (e.g., 5 mm or more, 10 mm or more,15 mm or more 20 mm or more) and/or 200 mm or less (e.g., 175 mm orless, 150 mm or less, 125 mm or less, 100 mm or less, 75 mm or less, 65mm or less, 55 mm or less, 45 mm or less). In certain embodiments, h isfrom 2 mm to 200 mm (e.g., from 5 mm to 175 mm, from 10 mm to 150 mm,from 15 mm to 125 mm, 20 mm to 100 mm). Typically, h can be adjusted bychanging the electrical potential applied to second lens 226 to adjustthe focal plane of lens 226, and translating sample 180 (via samplemanipulator 140) into the new focal plane of lens 226. The relativelylarge distance h permitted by microscope system 200 provides a number ofadvantages. For example, uneven samples with surface protrusions can beinvestigated using microscope system. Further, samples can also betilted at large angles with respect to the principal axis of ion beam192. For example, in some embodiments, the angle between a normal tosurface 181 of sample 180 and the principal axis of ion beam 192 is 50or more (e.g., 10° or more, 20° or more, 30° or more, 40° or more, 50°or more, 60° or more) and/or 85° or less (e.g., 80° or less, 75° orless, 70° or less, 65° or less). In certain embodiments, the anglebetween the normal to surface 181 of sample 180 and the principal axisof ion beam 192 is from 5° to 85° (e.g., from 10° to 80°, from 20° to70°, from 30° to 70°, from 40° to 60°). In addition, the relativelylarge distance h also permits a variety of detectors and other devicesto be positioned in close proximity to the region of incidence of ionbeam 192 on surface 181, and can allow for detection of particlesleaving the sample over a relatively large range of solid angles.Typically, this permits detection of stronger signals and detection ofmultiple different types of signals (e.g., using different types ofdetectors).

In some embodiments, second lens 226 is shaped as a right-angled conewith a cone half-angle of 10° or more (e.g., 15° or more, 20° or more,25° or more) and/or 50° or less (e.g., 45° or less, 40° or less. 35° orless). In certain embodiments, the cone half-angle of second lens 226 isfrom 10° to 50° (e.g., from 15° to 45°, from 20° to 40°). Relativelysmall cone half-angles for lens 226 provide a number of advantages,including a greater range of tilt angles of sample 180 with respect toion beam 192, and a larger volume of free space in the vicinity of theincident beam spot on surface 181 in which detectors and other devicescan be positioned.

As discussed above, typically, substantially only He ions generated viathe interaction of He atoms with one of the trimer atoms at apex 187 oftip 186 pass through aperture 224. However, in some embodiments,components in ion optics 130 (e.g., first lens 216 and/or alignmentdeflectors 220, 222 and/or aperture 224) can be set so that asubstantial fraction of He ions generated via the interaction of Heatoms with two of the trimer atoms pass through aperture 224. This canbe achieved, for example, by appropriate selection of the electricalpotentials applied to first lens 216 and/or deflectors 220, 222, and/orby changing the size of aperture 224 (e.g., by selecting a differentaperture opening on an aperture wheel or rod, as shown in FIGS. 15 and16, respectively). In certain embodiments, components in ion optics 130(e.g., first lens 216 and/or alignment deflectors 220, 222 and/oraperture 224) can be set so that a substantial fraction of He ionsgenerated via the interaction of He gas atoms with all three of thetrimer atoms pass through aperture 224. This can be achieved, forexample, by appropriate selection of the electrical potentials appliedto first lens 216 and/or deflectors 220, 222, and/or by changing thesize of aperture 224 (e.g., by selecting a different aperture opening onan aperture wheel or rod, as shown in FIGS. 15 and 16, respectively).

Optionally, one or more additional electrodes (e.g., lenses, deflectors,and/or other elements) can be positioned along the path of ion beam 192in ion optics 130. Additional electrodes can be positioned after secondlens 226, for example, or can be introduced between existing elements.The additional elements can be biased either positively or negativelywith respect to tip 186 to perform functions such as increasing ordecreasing the energy of the ions in ion beam 192 within ion optics 130and/or to change the trajectories of the ions. For example, one or moreaccelerating electrodes can be positioned in the vicinity of sample 180to change the energy with which the ions in ion beam 192 are incident onsample 180.

As another example, ion optics 130 can include a negatively biased(relative to the common external ground) column liner tube to increasethe energy of the ions in ion beam 192 at surface 181 of sample 180. Thetube can be biased at −50 kV or more (e.g., −25 kV or more, −15 kV ormore, −10 kV or more) and/or −1 kV or less (e.g., −3 kV or less, −5 kVor less) relative to the common external ground. In general, the tubecan be located at any position along axis 132 of ion optics 130 such as,for example, between aperture 224 and second lens 226. Certainadvantages can be realized by accelerating ions as they pass through ionoptics 130 including, for example, a reduction of the interaction timebetween like-charged ions, which can help to reduce the divergence ofion beam 192.

In some embodiments, the energy of the ions in ion beam 192 at surface181 of sample 180 can be increased or decreased by biasing sample 180(e.g., positively, if a decrease in the energy of the ions in ion beam192 is desired, or negatively, if an increase in the energy of the ionsin ion beam 192 is desired). At larger angles of incidence of ion beam192, the cylindrical asymmetry of the electric field produced by biasedsample 180 can produce a prism-like effect, where low energy ions in ionbeam 192 are deflected by a greater amount in the x- and y-directionsthan higher energy ions, resulting in an increase in spot size of ionbeam 192 on surface 181 of sample 180 and potentially other undesirableconsequences. In some embodiments, therefore, sample 180 is biased toalter the energy of ions in ion beam 192, and an angle between ion beam192 and a normal to surface 181 is less than 6° (e.g., less than 5°,less than 4°, less than 3°, less than 1°).

While certain embodiments of ion optics have been described, otherembodiments of ion optics can also be used. As an example, where acertain electrode type (e.g., octupole) has been described, one or moredifferent electrode types (e.g., quadrupole) may be used to achieve thesame effect. More generally, a variety of different ion optics systemscan be used in microscope system 200. In some embodiments, for example,ion optics 130 include only a single lens in addition to deflectors,apertures, and other ion optical elements. In certain embodiments, ionoptics 130 include first and second lenses with an aperturetherebetween.

As another example, in some embodiments, the ion optics include a firstlens, a second lens, an aperture between the first and second lenses, noelectrodes, and the ion optics are designed so that the first lens canreduce the divergence of the ion beam (e.g., such that the ion beam issubstantially aligned with the longitudinal axis of the ion opticssystem), the aperture can block a portion of the ion beam from passingtherethrough, and the second lens can help focus the ion beam to arelatively small spot size on the surface of the sample. In suchembodiments, the ions in the ion beam that reach the surface of thesample can be generated predominantly by the interaction of He atomswith only one atom of the trimer (as described above, for example). Insome embodiments, approximately equal numbers of ions in the ion beamthat reach the surface of the sample are generated via the interactionof He atoms with each of the three trimer atoms.

As an additional example, in certain embodiments, the ion optics includea first lens, a second lens, an aperture between the first and secondlenses, no electrodes, and the ion optics are designed so that the firstlens can focus the ion beam toward the center of the opening in theaperture, the aperture can allow the focused ion beam to diverge andpass therethrough, and the second lens can help focus the ion beam to arelatively small spot size on the surface of the sample. In suchembodiments, the ion beam that reaches the surface of the sample caninclude approximately equal numbers of ions generated by the interactionof gas atoms with each of the three atoms in the trimer. If the apex oftip 186 includes more than three atoms (e.g., five or more atoms, sevenor more atoms, nine or more atoms), the ion beam can includeapproximately equal numbers of ions generated via the interaction of gasatoms with each of the atoms at the apex of tip 186.

As a further example, in some embodiments, the ion optics include afirst lens, a second lens, an aperture between the first and secondlenses, no electrodes, and the ion optics are designed so that the firstlens can reduce the divergence of the ion beam and direct the lowdivergence beam toward the aperture, the aperture can allowsubstantially all the ions in the ion beam to pass therethrough, and thesecond lens can help focus the ion beam to a relatively small spot sizeon the surface of the sample. In such embodiments, the ion beam thatreaches the surface of the sample can include approximately equalnumbers of ions generated via the interaction of gas atoms with each ofthe three atoms in the trimer. If the apex of tip 186 includes more thanthree atoms (e.g., five or more atoms, seven or more atoms, nine or moreatoms), the ion beam can include approximately equal numbers of ionsgenerated via the interaction of gas atoms with each of the atoms at theapex of tip 186.

As another example, in certain embodiments, the ion optics include afirst lens, a second lens, an aperture between the first and secondlenses, no electrodes, and the ion optics are designed so that the firstlens can partially focus the ion beam toward the aperture, the aperturecan block a portion of the ions in the ion beam from passingtherethrough (but still allow a relatively large fraction of the ions inthe ion beam to pass therethrough), and the second lens can help focusthe ion beam to a relatively small spot size on the surface of thesample. In such embodiments, the ion beam that reaches the surface ofthe sample can include approximately equal numbers of ions generated viathe interaction of gas atoms with each of the three atoms in the trimer.If the apex of tip 186 includes more than three atoms (e.g., five ormore atoms, seven or more atoms, nine or more atoms), the ion beam caninclude approximately equal numbers of ions generated via theinteraction of gas atoms with each of the atoms at the apex of tip 186.

D. Tip Tilt and Translation Mechanism

Tip manipulator 208 is configured to permit both translation of tip 186in the x-y plane, and tilting of tip 186 with respect to axis 132 of ionoptics 130. FIG. 17 is a cross-sectional view of a portion of microscopesystem 200 including tip 186, support assembly 520 and an embodiment ofa tip manipulator. Tip manipulator 208 includes a shaft 502, a dome 504,a shoulder 510 and a translator 514. Translator 514 is connected toshaft 502, which is dimensioned to fit through an opening 516 inshoulder 510. Shaft 502 is further connected to base 508, which in turnis connected to assembly 520. Shoulder 510 is in a fixed positionrelative to dome 504 by static frictional forces between surfaces 512and 513, and translator 514 is in a fixed position relative to shoulder510 by static frictional forces between surfaces 518 and 519.

Tip manipulator 208 provides for translation of tip 186 in the x-yplane. To translate tip 206, a high pressure gas is introduced intoinlet 503. The high pressure gas introduced into inlet 503 can be a gassuch as room air, for example. Typically, the gas can be introduced at apressure of 50 pounds per square inch (psi) or more (e.g., 75 psi ormore, 100 psi or more, 125 psi or more). As a result of introducing thehigh pressure gas, a force is applied to translator 514 in the −zdirection, away from shoulder 510. The applied force lessens (but doesnot reduce to zero) the frictional force between surfaces 518 and 519,and permits repositioning of translator 514 with respect to shoulder 510by applying a lateral force in the x-y plane. Tip 186 is translated inthe x-y plane when translator 514 is repositioned. When tip 186 is inits new position, the supply of high pressure gas is turned off andstrong static frictional forces between surfaces 518 and 519 arere-established by evacuating the interior of tip manipulator 208 usingone or more vacuum pumps. Tip 186 is rigidly fixed in position as aresult of the re-established strong frictional forces.

Tip manipulator 208 also provides for tilting of tip 186 with respect toaxis 132 of ion optics 130. To tilt tip 186, a high pressure gas isintroduced into inlet 505. The high pressure gas introduced into inlet505 can be a gas such as room air, for example. Typically, the gas canbe introduced at a pressure of 50 pounds per square inch (psi) or more(e.g., 75 psi or more, 100 psi or more, 125 psi or more). As a result ofintroducing the high pressure gas, a force is applied to shoulder 510 inthe −z direction, away from dome 504. The applied force lessens (butdoes not reduce to zero) the frictional force between surfaces 512 and513. Shoulder 510 can then be re-positioned with respect to dome 504 byapplying a lateral force to translate shoulder 510 in a directionindicated by arrows 506. Translation of shoulder 510 corresponds torelative movement along the curved surface of dome 504. As a result ofthis movement, the angle between axes 132 and 207 (which corresponds tothe tilt angle of tip 186) changes. When adjustment of the tilt of tip186 is complete, the supply of high pressure gas is turned off andstrong static frictional forces between surfaces 512 and 513 arere-established by evacuating the interior of tip manipulator 208. Tip186 is rigidly fixed in position as a result of the re-establishedstrong frictional forces.

In some embodiments, as shown in FIG. 17, tip manipulator 208 isconfigured so that the center of the radius of curvature, R, of dome 504coincides with the position of the apex of tip 186. As a result, whentip 186 is tilted to change the angle between axes 132 and 207,translation of tip 186 in the x-y plane does not occur. As a result, tipmanipulator 208 can be used to align the trajectories of ions generatedvia the interaction of gas atoms with one of the tip atoms with thelongitudinal axis of first lens 216 without causing translation of tip186 with respect to the axis of first lens 216.

In certain embodiments, tip manipulator 208 can be configured to permitrotational motion about additional axes. For example, in the embodimentshown in FIG. 17, when high pressure gas is introduced into inlet 503 toreduce the frictional force between surfaces 518 and 519 and permittranslation of translator 514 in the x-y plane, translator 514 can alsobe rotated about axis 207 by applying a suitable torque to translator514. This rotation can be performed separately from, or in addition to,translation of tip 186 and tilt adjustment of tip 186.

E. Sample Stage

Referring again to FIG. 5, microscope system 200 includes a samplemanipulator 140 for supporting and positioning sample 180. In responseto control signals from electronic control system 170, samplemanipulator 140 can translate sample 180 in each of the x-, y-, andz-directions. In some embodiments, sample manipulator 140 can alsorotate sample 180 in the x-y plane in response to control signals.Further, in certain embodiments, sample manipulator 140 can tilt sample180 out of the x-y plane in response to suitable control signals. Eachof these degrees of freedom can be independently adjusted to achieve asuitable orientation of sample 180 with respect to ion beam 192.

As described in more detail below, in some embodiments, samplemanipulator 140 can be biased, either positively or negatively withrespect to the common external ground, by applying a relatively smallelectrical potential to manipulator 140. For example, in someembodiments, a positive potential bias of 5 V or more (e.g., 10 V ormore, 20 V or more, 30 V or more, 40 V or more, 50 V or more) relativeto the common external ground can be applied to manipulator 140 toassist in preventing positively charged He ions from adhering to surface181 of sample 180. In certain embodiments, a negative potential bias of−200 V or more (e.g., −150 V or more, −100 V or more, −50 V or more, −40V or more, −30 V or more, −20 V or more, −10 V or more, −5 V or more)relative to the common external ground can be applied to manipulator 140to assist, for example, in accelerating secondary electrons (that leavesurface 181 of sample 180 via the interaction of the ions with sample180) away from the sample, ensuring that the secondary electrons can bedetected by a suitably configured detector. In general, the potentialapplied to manipulator 140 can be chosen as desired according to theparticular material under study, the He ion current, and exposure timeof the sample.

F. Detectors

Detectors 150 and 160 are depicted schematically in FIG. 5, withdetector 150 positioned to detect particles from surface 181 of sample180 (the surface on which the ion beam impinges), and detector 160positioned to detect particles from surface 183 of sample 180. Ingeneral, a wide variety of different detectors can be employed inmicroscope system 200 to detect different particles, and a microscopesystem 200 can typically include any desired number of detectors. Theconfiguration of the various detector(s) can be selected in accordancewith particles to be measured and the measurement conditions. In someembodiments, a spectrally resolved detector may be used. Such detectorsare capable of detecting particles of different energy and/orwavelength, and resolving the particles based on the energy and/orwavelength of each detected particles. In certain embodiments, aspectrally resolved detector includes componentry capable of directingparticles to different regions of the detector based on the energyand/or wavelength of the particle.

Certain exemplary detectors and arrangements of detectors are describedbelow.

(i) Everhart-Thomley Detectors

An Everhart-Thomley (ET) detector can be used to detect secondaryelectrons, ions, and/or neutral particles. FIG. 18 shows a schematicdiagram of an ET detector 600 that includes a particle selector 601, aconversion material 602, a support 604, a photon detector 606, andvoltage sources 607 and 608.

Particle selector 601 is formed of an electrically conductive material.In some embodiments, for example, particle selector 601 can be a metalgrid or mesh with a metal fill-factor of less than approximately 30%(e.g., less than 25%, less than 20%, less than 10%, less than 5%).Because the grid is predominantly open space, particles impinging on thegrid can pass through relatively unobstructed.

In certain embodiments, particle selector 601 is formed of a metal ringor tube. For example, particle selector 601 can be a ring or tube thatis substantially cylindrical in shape, with an interior opening thatpermits particles to pass through the ring or tube. The ring or tube canbe formed of a highly conductive metal such as copper or aluminum, forexample.

More generally, particle selector 601 can be formed from any openelectrode structure that includes a passage for particles to passthrough. Particle selector 601 can be formed from one or moreelectrodes, and potentials applied to the one or more electrodes cangenerally be selected as desired according to the type of particlesbeing measured.

Conversion material 602 is formed of a material that, upon interactionwith a charged particle (e.g., an ion, an electron) can form a photon.Exemplary materials include phosphor materials and/or scintillatormaterials (e.g., crystalline materials, such as yttrium-aluminum-garnet(YAG) and yttrium-aluminum-phosphate (YAP). Support 604 is formed of amaterial that is relatively transparent to photons formed by conversionmaterial 602.

During operation, voltage source 607 applies a voltage of relativelysmall magnitude (e.g., 500 V or less, such as from 100 V to 500 V) toparticle selector 601 (formed of a conductive material), and voltagesource 608 applies a voltage of relatively large magnitude (e.g., 5 kVor more, 10 kV or more) to conversion material 602. In embodiments inwhich the ET detector is used to measure electrons from sample 180(e.g., secondary electrons), the sign of the voltage applied to particleselector 601 and conversion material 602 is positive with respect tosample 180. In embodiments in which the ET detector is used to measureions from sample 180 (e.g., secondary ions, scattered ions), the sign ofthe voltage applied to particle selector 601 and conversion material 602is negative with respect to sample 180. In certain embodiments, sample180 can also be biased (with respect to the common external ground) toassist in delivering particles from sample 180 to detector 600. Forexample, when the ET detector is used to measure secondary electronsfrom sample 180, the sample can be negatively biased relative to thecommon external ground. Applying a negative potential bias tomanipulator 140 may be particularly useful, for example, when detectingsecondary electrons generated in a high aspect ratio (e.g., deep) holeor via in the sample. The negative potential bias relative to the commonexternal ground can assist in accelerating electrons out of the hole orvia and away from the sample, making detection of the electrons easier.In the absence of the negative bias, many of the secondary electronsmight instead re-enter the sample at points along the hole or via walls,never escaping the hole or via to be detected.

Sample 180 can be positively biased, for example, when the ET detectoris used to measure ions from the sample. The magnitude of the electricalpotential applied to bias the sample can be 5 V or more (e.g., 10 V ormore, 15 V or more, 20 V or more, 30 V or more, 50 V or more, 100 V ormore).

Charged particles 610 (e.g., electrons or ions) from sample 180 areattracted to particle selector 601, pass through particle selector 601,and are accelerated toward conversion material 602. Charged particles610 then collide with conversion material 602, generating photons 612.Photons 612 pass through support 604 and are detected by photon detector606.

While operation of an ET detector has been described with respect tomeasuring charged particles, an ET detector can also be used to detectneutral particles because, in general, particles impinging on conversionmaterial 602 do not have to be charged to generate photons 612. Inparticular, primary atoms from sample 180, impinging on conversionmaterial 602, can generate photons 612 for detection by photon detector606. Photon detector 606 can be, for example, a photomultiplier tube(PMT), a diode, a diode array, or a CCD camera.

An ET detector can be located at any position relative to sample 180 todetect neutral or charged particles. Typically, for example, an ETdetector is positioned adjacent to second lens 226 of ion optics 130.Optionally, an ET detector can also be positioned such that it is tilteddownward slightly towards sample 180 (e.g., in a similar configurationas that depicted for detector 150 in FIG. 5).

In certain embodiments, an ET detector can be positioned in the vicinityof surface 183 of sample 180. Such a configuration may be desirable, forexample, when seeking to measure secondary electrons from sample 180that emerge from surface 183 (e.g., after being transmitted throughsample 180). In such embodiments, the ET detector can have aconfiguration that is similar to the configuration of detector 160 inFIG. 5.

(ii) Photon Detectors

To detect photons generated by the interaction of the ions with sample180, a standard photon detector such as a PMT can be used. If the photonflux emanating from sample 180 is sufficiently large, less sensitivephoton detectors such as diodes, diode arrays, and CCD cameras can beused.

In some embodiments, the photon detector can also include variousoptical elements that can be configured, for example, to isolate aparticular optical signal of interest from among other optical signals.For example, in certain embodiments, the photon detector can includeoptical elements such as filters to select particular wavelength bandsin the photon signal emerging from sample 180, which can providematerial constituent information about sample 180. The filters can, forexample, block photons of undesired wavelengths (e.g., by absorbingphotons of undesired wavelengths, by reflecting photons of undesiredwavelengths, by diverting photons of undesired wavelengths). In someembodiments, the optical elements can provide spectral resolution (e.g.,to measure the spectrum of photons generated by sample 180) bydispersing different wavelengths spatially (e.g., diffractive elementssuch as one or more gratings, and/or refractive elements such as one ormore prisms, and/or one or more spectrometer systems that providewavelength-resolved detection of photons). In some embodiments, thephoton detector can include polarization manipulating elements such aswaveplates and/or polarizers. These polarization manipulating elementscan be configured to permit photons having only a selected polarizationstate to reach the PMT, for example, allowing polarization-selectivedetection of the photon signal emerging from sample 180 (e.g., to assistin determining crystalline orientation information for sample 180). Incertain embodiments, the photon detector can also include opticalelements such as mirrors, lenses, beamsplitters, and other elements forre-directing and manipulating incident photons (e.g., to increase thesolid angle of the photons that are detected).

In general, photon detectors can be positioned to detect photons at anydesired angle and distance from sample 180. For example, in certainembodiments, a photon detector can be positioned to detect photonsemerging from surface 181 (the surface of sample 180 upon which ion beam192 is incident), or from surface 183 (the surface of sample 180opposite to the surface upon which ion beam 192 is incident).Optionally, multiple photon detectors can be used and configured todetect photons from surfaces 181 (the surface on which the ion beamimpinges), 183 (the surface on the opposite side from where the ion beamimpinges) and/or other surfaces of sample 180.

For some samples, photons are scattered in particular directionsaccording to selection rules for optical processes occurring in sample180, and angle-resolved measurement of the photon yield from sample 180can provide, for example, material constituent information about sample180.

(iii) Microchannel Plate Detectors

In some embodiments, a microchannel plate detector can be used toamplify a flux of secondary electrons, neutral atoms, or ions fromsample 180. Microchannel plates are typically formed from materials suchas fused silica, and generally include a large number of small diameterchannels arranged in the form of an array. Particles enter individualchannels and collide with channel walls, generating free electrons.Typically, multiple free electrons are generated on each collision of aparticle (neutral atom, ion, or electron) with a channel wall. As aresult, a cascaded electron signal corresponding to an amplification ofthe input particle signal exits the microchannel plate.

Microchannel plate-based detectors (which can include one or moremicrochannel plates) can be configured to detect ions, secondaryelectrons, and/or neutral atoms from sample 180. Neutral particlesand/or ions (e.g., secondary ions and atoms, scattered ions and primaryatoms) formed from sample 180 typically leave surface 181 of sample 180(the surface on which the ion beam impinges). Accordingly, microchannelplate-based detectors configured to measure neutrals and/or ions fromsample 180 are generally located at positions similar to the position ofdetector 150 depicted in FIGS. 1 and 5. However, in certain embodiments,neutral particles and/or ions (e.g., transmitted ions) can beinvestigated. In such embodiments, a microchannel plate-based detectorcan be located at positions similar to the position of detector 160 inFIGS. 1 and 5. Secondary electrons can be detected either from surface181 (the surface on which the ion beam impinges) and/or surface 183 ofsample 180 (the surface on the opposite side from where the ion beamimpinges), and microchannel plate-based detectors configured to detectsecondary electrons from sample 180 are located at positions similar todetector 150 and/or detector 160 as depicted in FIGS. 1 and 5.

Microchannel plates amplify an incoming particle signal and convert theincoming signal to an outgoing electron signal. To visualize theoutgoing electron signal, microchannel plate-based detectors can alsoinclude a conversion material, a screen, and a photon detector (seediscussion above).

In some embodiments, microchannel plates are affixed directly toelements of ion optics 130. FIG. 19 shows a cross-sectional view of amicrochannel plate detector 620 mounted directly to second lens 226.Second lens 226 has a conical shape, with a flat lower surface 622.Detector 620 is mounted directly to surface 622. When sample 180 isexposed to ion beam 192, ions, secondary electrons, and/or neutral atomsfrom sample 180 (collectively indicated by arrow 624) can be detected bymicrochannel plate detector 620. Detector 620 registers a current thatis proportional to the detected particle flux, which can be conveyed toelectronic control system 170.

(iv) Conversion Plates

In some embodiments, a conversion plate can be used to detect ions(e.g., scattered ions, secondary ions) from sample 180 or neutralparticles (e.g., primary neutral He atoms) from sample 180. Typically, aconversion plate can be formed from a thin foil material that, whenstruck by an incident ion or atom, has a high secondary electron yield.An example of such a material is platinum. The secondary electron yieldproduces an abundance of secondary electrons that are readily detected,for example, by an appropriate electron detector configured, forexample, as detectors 150 and/or 160 (FIGS. 1 and 5).

(v) Channeltron Detectors

Channeltron detectors can also be used to detect particles such aselectrons, ions and neutral atoms leaving sample 180. Channeltrondetectors function by amplifying particle signals through multipleinternal collisions in a manner similar to that described in connectionwith microchannel plate detectors. Measurement of relatively weaksecondary electron, ion, or neutral atom fluxes from sample 180 ispossible by measuring the amplified particle signals that are output bya channeltron detector (e.g., using electronic control system 170). Whenmeasuring secondary electrons from sample 180, a channeltron detectorcan be located in a position similar to that depicted for detector 150and/or detector 160 in FIGS. 1 and 5. Typically, for the measurement ofions and/or neutral particles from sample 180, a channeltron detector islocated in a position similar to the position of detector 150 and/or theposition of detector 160 as depicted in FIGS. 1 and 5.

(vi) Phosphor Detectors

Phosphor-based detectors, which include a thin layer of a phosphormaterial deposited atop a transparent substrate, and a photon detectorsuch as a CCD camera, a PMT, or one or more diodes, can be used todetect electrons, ions and/or neutral particles from sample 180.Particles strike the phosphor layer, inducing emission of photons fromthe phosphor which are detected by the photon detector. Phosphor-baseddetectors can be arranged in positions similar to those of detector 150and/or detector 160 as depicted in FIGS. 1 and 5, depending upon thetype of particle that is measured (see discussion above).

(vii) Solid State Detectors

Solid state detectors can be used to detect secondary electrons, ions,and/or neutral atoms from sample 180. A solid state detector can beconstructed from a sensor formed of a material such as silicon, or adoped silicon material. When incident particles strike the sensor,electron-hole pairs are created in the sensor material, producing acurrent that can be detected by electronic control system 170. Thenumber of electron-hole pairs generated by an incident particle, andtherefore the corresponding magnitude of the current produced, dependsin part upon the particle's energy. Thus, a solid state detector can beparticularly useful for energy measurements of particles, which can beespecially advantageous when detecting high energy particles (e.g.,scattered He ions and neutral He atoms) from sample 180.

(viii) Scintillator Detectors

Similar to phosphor-based detectors, scintillator-based detectorsinclude a scintillator material that generates photons in response tobeing struck by an incident particle (electron, ion, or neutral atom).Suitable scintillator materials include, for example, YAG and YAP. Thephoton yield in scintillator-based detectors depends on the energy ofthe incident particles. As a result, a scintillator detector can beparticularly useful for energy measurements of particles, which can beespecially advantageous when detecting high energy particles (e.g.,scattered He ions and neutral He atoms) from sample 180.

(ix) Energy Detectors for Ions

A variety of different detectors and detection schemes can beimplemented to measure energies of ions (e.g., scattered He ions) fromsample 180. Electrostatic prism detectors, in which an electric and/ormagnetic field is used to deflect incident ions, where the amount ofdeflection depends on the energy of the ions, can be used to spatiallyseparate ions with different energies. Magnetic prism detectors may alsobe used to spatially separate ions based on the energy of the ions. Anyof the suitable detectors discussed above (e.g., microchannel plates,channeltrons, and others) can then be used to detect the deflected ions.

Quadrupole detectors can also be used to analyze energies of ions fromsample 180. In a quadrupole detector, a radio-frequency (RF) fieldwithin the quadrupole ensures that ions having a chosen mass and energypropagate along a straight, undeflected trajectory within thequadrupole. Ions with a different mass and/or energy propagate along acurved trajectory within the quadrupole. From the deflected position ofions within the quadrupole analyzer, energies of the ions can bedetermined.

In some embodiments, ion energy can be determined by placing apositively biased particle selector (e.g., a screen or mesh ofelectrically conductive material, or a cylindrical metal tube or ring)along the flight path of the ions and in front of the detector. Themagnitude of the electrical potential applied to particle selector 601can initially be very high (e.g., a value certain to prevent ions fromsample 180 from passing therethrough), and the magnitude of theelectrical potential can be reduced while using an appropriate detector(see discussion above) to detect the ions. The current of ions thatreach the detector as a function of the magnitude of the potential biason the particle selector can be used to determine information about theenergy of the ions.

(x) Energy Detectors for Electrons

A variety of different detectors and detection schemes can beimplemented to measure energies of electrons (e.g., secondary electrons)from sample 180. Prism detectors, in which an electric and/or magneticfield is used to deflect incident electrons, and where the amount ofdeflection depends on the energy of the electrons, can be used tospatially separate electrons with different energies. Any of thesuitable detectors discussed above can then be used to detect thedeflected electrons.

In some embodiments, electron energies can be determined by placing anegatively biased particle selector (e.g., a screen or mesh ofelectrically conductive material, or a cylindrical metal tube or ring)along the flight path of the electrons and in front of the detector. Themagnitude of the electrical potential of the particle selector caninitially be very high (e.g., a value certain to prevent the electronsfrom sample 180 from passing therethrough), and the magnitude of theelectrical potential can be reduced while using an appropriate detector(see discussion above) to detect the electrons. The electron currentthat reaches the detector as a function of the magnitude of the appliedelectrical potential on the particle selector can be used to determineinformation about the energies of the electrons.

(xi) Time-of-Flight Detectors

The detectors disclosed above can also be configured to measuretime-of-flight information for secondary electrons, ions, and neutralatoms. To perform time-of-flight detection, ion beam 192 is operated inpulsed mode. Ion beam 192 can be pulsed, for example, by rapidlychanging the electrical potential applied to one or both of deflectors220 and 222. By increasing these potentials, for example, ion beam 192can be diverted from its usual path in ion optics 130 such that ion beam192 is temporarily blocked by aperture 224. If the potentials ofdeflectors 220 and 222 are then returned to their normal values for ashort time before being increased again, a pulse of He ions can bedelivered to sample 180.

At the same time, detectors 150 and 160 can be synchronized to a clocksignal from electronic control system 170 that is based upon thetemporal variation in potentials applied to deflectors 220 and/or 222.As a result, the time interval between the launch of a He ion pulse andthe detection of particles from sample 180 can be accurately measured.From known information about the time of propagation of the He ion pulsewithin ion optics 130, the time-of-flight of the detected particlesbetween sample 180 and detectors 150 and/or 160 can be determined.

(xii) Angle-Dependent Measurements

In addition to measuring relative abundances and energies of particlesfrom sample 180, angle-dependent scattering information can be obtainedusing the detectors disclosed above. Typically, to acquireangle-dependent information, a detector is affixed to a mount (e.g., aswivel mount) that permits movement of the detector throughout a rangeof solid angles about sample 180. At a given orientation with respect tosample 180 that corresponds to a particular solid angle, abundanceand/or energy measurements of particles are recorded. The detector issequentially re-positioned at different solid angles and themeasurements are repeated to determine the angular dependence of themeasured quantities. In some embodiments, a limiting aperture such as apinhole can be placed in front of the detector in the path of thescattered particles to further restrict the range of angles over whichmeasurement of particles from sample 180 occurs.

G. Operational Parameters

Ion beam 192 can have a relatively small spot size on surface 181 ofsample 180. For example, in some embodiments, the spot size of ion beam192 on surface 181 of sample 180 can have a dimension of 10 nm or less(e.g., nine nm or less, eight nm or less, seven nm or less, six nm orless, five nm or less, four nm or less, three nm or less, two nm orless, one nm or less). In certain embodiments, the spot size of ion beam192 on surface 181 of sample 180 has a dimension of 0.05 nm or more(e.g., 0.1 nm or more, 0.2 nm or more, 0.25 nm or more, 0.5 nm or more,0.75 nm or more, one nm or more, two nm or more, three nm or more). Insome embodiments, the spot size of ion beam 192 on surface 181 has adimension of from 0.05 nm to 10 nm (e.g., from 0.1 nm to 10 nm, 0.2 nmto 10 nm, 0.25 nm to 3 nm, 0.25 nm to one nm, 0.1 nm to 0.5 nm, 0.1 nmto 0.2 nm). As used herein, spot size is determined as follows withreference to FIGS. 20A-20C. An island 1700 formed of gold and having adimension of from 50 nm to 2000 nm is disposed on a carbon surface 1710.The gold island is formed, for example, by vapor deposition of gold ontothe carbon surface. Measurement samples that include gold islandsdeposited on carbon, suitable for the resolution measurements describedherein, are available commercially from Structure Probe Inc. (WestChester, Pa.), for example. The ion microscope is operated such that itmoves ion beam 192 linearly across a portion of the gold island, as wellas the portions of the carbon surface on one side of the gold island(arrow 1730). The intensity of secondary electrons is measured as afunction of the location of the ion beam (FIG. 20C). Asymptotic lines1740 and 1750 are calculated (or drawn) corresponding to the averagetotal abundance values for the carbon and gold, and vertical lines 1760and 1770 are calculated (or drawn) corresponding to the locations wherethe total abundance is 25% and 75%, respectively, of the abundancedifference between asymptotic lines 1740 and 1750. The spot size of ionmicroscope 200 is the distance between lines 1760 and 1770.

In general, the current of ion beam 192 at surface 181 of sample 180 isone nA or less (e.g., 100 pA or less, 50 pA or less), and/or 0.1 fA ormore (e.g., one fA or more, 10 fA or more, 50 fA or more, 100 fA ormore, one pA or more, 10 pA or more). For example, in some embodiments,the current of ion beam 192 at surface 181 of sample 180 is from 0.1 fAto one nA (e.g., from 10 fA to 100 pA, from 100 fA to 50 pA). In certainembodiments, it can be desirable to use a relatively low beam currentwhen imaging a sample. For example, in some biological and/orpharmaceutical applications, it may be more important to use a lowcurrent to image in the sample (e.g., to reduce possible damage to thesample). In such embodiments, one current can be used to prepare the gasfield ion microscope for use (e.g., a current of 10 fA or more), and adifferent current can be used to image the sample (e.g., a current ofless than one fA, such as 0.1 fA).

Generally, ion beam 192 has an energy spread at surface 181 of sample180 of five eV or less (e.g., four eV or less, three eV or less, two eVor less, one eV or less, 0.5 eV or less). In some embodiments, ion beam192 has an energy spread at surface 181 of sample 180 of 0.1 eV or more(e.g., 0.2 eV or more, 0.3 eV or more, 0.4 eV or more). For example, ionbeam 192 can have an energy spread at surface 181 of sample 180 of from0.1 eV to five eV (e.g., from 0.1 eV to three eV, from 0.1 eV to oneeV).

Ion beam 192 can have a relatively high brightness at surface 181 ofsample 180. For example, ion beam 192 can have a brightness of 1×10⁹A/cm²sr (e.g., 1×10¹⁰ A/cm² sr or more, 1×10¹¹ A/cm² sr or more) atsurface 181 of sample 180. In some embodiments, the brightness can beincreased by increasing the gas pressure adjacent to tip 186 and/ordecreasing the temperature of tip 186. As referred to herein, thebrightness of an ion beam is measured as follows. The FWHM of thedistribution of ion trajectories in ion beam 192—in a region of spacebetween extractor 190 and first lens 216 where the net electric field isrelatively small and the ion trajectories are nearly straight lines—isdetermined in both the x- and y-directions. A total of 100 iontrajectories that fall within the FWHM width in both the x- andy-directions are chosen at random from the distribution of iontrajectories in ion beam 192. Each of the 100 ion trajectories is nearlya straight line, and is projected back toward tip apex 187. The spatialextent of the trajectories at a particular point z_(t) along the z-axisis assessed by constructing, in a plane Z_(t) parallel to the x-y planeand passing through point z_(t), the smallest-diameter circle thatencloses all of the points of intersection of the back-propagatedtrajectories with the plane Z_(t). The diameter of the smallest-diametercircle is d_(s). Typically, for points z_(t) closer to tip apex 187,d_(s) will be smaller and for points z_(t) closer to sample 180, d_(s)will be larger. At a particular point z_(t)=z₀, d_(s) will be a minimumvalue d₀. That is, the spatial extent of the trajectories in a planeparallel to the x-y plane will be a minimum. The diameter d₀ of theminimum-diameter circle at point z₀ is referred to as the virtual sourcesize of microscope system 200. Next, the divergence and beam current ofion beam 192 in the FWHM region of ion beam 192 between extractor 190and first lens 216, as discussed above, are measured. Finally,brightness is calculated as beam current divided by the product of thevirtual source size and the solid divergence angle of ion beam 192.

Ion beam 192 can have a relatively high reduced brightness at surface181 of sample 180. For example, ion beam 192 can have a reducedbrightness of 5×10⁸ A/m²srV or more (e.g., 1×10⁹ A/cm²srV or more,1×10¹⁰ A/cm²srV or more) at surface 181 of sample 180. As referred toherein, the reduced brightness of an ion beam is the brightness of theion beam divided by the average energy of the ions in the ion beam atthe position where the beam current is measured

Ion beam 192 can have a relatively low etendue at a distal end 193 ofextractor 190. For example, ion beam 192 can have an etendue of 5×10⁻²¹cm² sr or less (e.g., 1×10⁻²² cm²sr or less, 1×10⁻²³ cm² sr or less,1×10⁻²³ cm² sr or less, 1×10⁻²⁴ cm²sr or less) at distal end 193 ofextractor 190. As referred to herein, the etendue of an ion beam iscalculated as the mathematical product of the reciprocal of thebrightness and the beam current.

Ion beam 192 can have a relatively low reduced etendue at a distal end193 of extractor 190. For example, ion beam 192 can have a reducedetendue of 1×10⁻¹⁶ cm²sr or less (e.g., 1×10⁻¹⁷ cm²sr or less, 1×10⁻¹⁸cm²sr or less, 1×10⁻¹⁹ cm² sr or less) at distal end 193 of extractor190. Reduced etendue of an ion beam is the mathematical product of theetendue of the ion beam and the ratio of the average energy-to-charge ofions in the ion beam at the position where the beam current is measured.

Ion beam 192 can have a relatively low angular convergence with respectto surface 181 of sample 180. For example, in some embodiments, theconvergence half angle of ion beam 192 can be 5 mrad or less (e.g., 1mrad or less, 0.5 mrad or less, 0.1 mrad or less), and/or 0.05 mrad ormore. As referred to herein the convergence half angle of an ion beam isdetermined as follows. A sample that includes a gold island atop acarbon substrate, as described above, is mounted in ion microscope 200and translated in the z-direction so that the position of the focus ofion beam 192 lies, as nearly as possible, at the highest elevation pointalong a diameter of the gold island. Ion beam 192 is then translatedlinearly along the diameter of the gold island and the focused spotsize, s_(f), of the ion beam is measured, as described above. The sampleis then translated in the +z direction, away from ion optics 130, bys_(z)=1 μm, and ion beam 192 is translated linearly along the samediameter of the gold island to measure the defocused spot size, s_(d),of ion beam 192. The convergence angle η can then be determinedtrigonometrically from the measurements of the focused and defocusedspot sizes, along with the translation distance, as$\eta = {2\quad{\sin^{- 1}\left( \frac{s_{d} - s_{f}}{2s_{z}} \right)}}$The convergence half angle of ion microscope 200 is η/2.

Ion microscope 200 can be highly reliable. As an example, in someembodiments, the He ion source (tip 186, extractor 190 and optionallysuppressor 188) is capable of continuously interacting with gas atoms togenerate an ion beam for a time period of one week or more (e.g., twoweeks or more, one month or more, two months or more) without removingtip 186 from the system. In some embodiments, during the time periodthat the He ion source is continuously interacting with gas atoms togenerate an ion beam, the current of ion beam 192 at surface 181 ofsample 180 varies by 10% or less (e.g., 5% or less, 1% or less) perminute.

As another example, in some embodiments, the gas field ion source (tip186, extractor 190 and optionally suppressor 188) is capable ofinteracting with gas atoms to generate an ion beam for a time period ofone week or more (e.g., two weeks or more, one month or more, two monthsor more) with a total interruption time of 10 hours or less (e.g., fivehours or less, two hours or less, one or less). In such embodiments, thegas field ion source may interact with gas atoms to generate the ionbeam continuously for the entire time period (corresponding to a totalinterruption time of zero hours), but this is not necessary. Forexample, during the time period, there may be times when the gas fieldion microscope is not interacting with gas atoms to generate an ionbeam. Such time periods correspond to an interruption time. During thetime period, such interruption times may occur one time or more than onetime (e.g., two times, three, times, four times, five times, six times,seven times, eight times, nine times, 10 times). The interruptions maybe due, for example, to scheduled maintenance, unexpected maintenance,and/or down time between shifts (e.g., overnight down time). During thetime period, the total of the interruption times is the totalinterruption time. As an example, if during the time period there arethree interruption times, each of one hour, then the total interruptiontime is three hours. As another example, if during the time period thereis only one interruption time and it is three hours long, then the totalinterruption time is three hours. As a further example, if during thetime period there are two interruption times, with the firstinterruption time being an hour and the second interruption time beingtwo hours, then the total interruption time is three hours. In someembodiments, for those times during the time period when the gas fieldion source is interacting with gas atoms to generate an ion beam, thecurrent of ion beam 192 at surface 181 of sample 180 varies by 10% orless (e.g., 5% or less, 1% or less) per minute.

Ion microscope 200 can have a relatively good resolution. For example,in some embodiments, the resolution of ion microscope 200 can be 10 nmor less (e.g., nine nm or less, eight nm or less, seven nm or less, sixnm or less, five nm or less, four nm or less, three nm or less, two nmor less, one nm or less). In certain embodiments, the resolution of ionmicroscope 200 can be 0.05 nm or more (e.g., 0.1 nm or more, 0.2 nm ormore, 0.25 nm or more, 0.5 nm or more, 0.75 nm or more, one nm or more,two nm or more, three nm or more). In some embodiments, the resolutionof ion microscope 200 can be from 0.05 nm to 10 nm (e.g., from 0.1 nm to10 nm, 0.2 nm to 10 nm, 0.25 nm to 3 nm, 0.25 nm to one nm, 0.1 nm to0.5 nm, 0.1 nm to 0.2 nm). As used herein, the resolution of an ion beamrefers to the size of the smallest feature that can be reliably measuredfrom images obtained using the ion microscope. A size of a feature isreliably measured if it can be determined to within an error of 10% orless of the actual size of the feature, and with a standard deviation inthe measured size of less than 5% of the actual size of the feature,from ten images of the feature obtained under similar conditions.

Ion microscope 200 can be used to take a good quality image in arelatively short period of time. For example, ion microscope 200 canhave a quality factor of 0.25 or more (e.g., 0.5 or more, 0.75 or more,one or more, 1.5 or more, two or more). As referred to herein, thequality factor is determined as follows. A planar sample, one half ofwhich is formed of silicon (Si) and the other half of which is formed ofcopper (Cu), with a boundary between the materials being a straight lineacross the sample, is positioned so that the boundary is orientedparallel to the y-axis. The sample is imaged pixel-by-pixel bysub-dividing the surface of the sample into an x-y array of 512 pixelsby 512 pixels. The dwell time per pixel is 100 ns during themeasurement. The total abundance of secondary electrons from the sampleis measured as a function of the position of the ion beam on the surfaceof the sample. For image pixels that correspond to Si in the sample, anaverage pixel intensity G₁ is determined, along with a standarddeviation SD₁ from the distribution of Si pixel intensities. For imagepixels that correspond to Cu in the sample, an average pixel intensityG₂ is determined, along with a standard deviation SD₂ from thedistribution of Cu pixel intensities. The quality factor is calculatedaccording to the equation$\frac{G_{1} - G_{2}}{\sqrt{{SD}_{1} \cdot {SD}_{2}}}$

Surface 181 of sample 180 can undergo relatively little damage whenexposed to ion beam 192. For example, surface 181 of sample 180 can havea value of 25 nm or less (e.g., 20 nm or less, 15 nm or less, 10 nm orless, five nm or less) according to the damage test. As referred toherein, the damage test is performed as follows. An atomically flatsilicon (99.99% purity) sample with a four square μm field of view isimaged for 120 seconds while rastering the ion beam across the surfaceof the sample pixel-by-pixel using an ion beam current at the sample of10 pA and a spot size of the ion beam at the sample of 10 nm or less.The four square μm field of view is broken into a 512 pixel by 512 pixelarray for rastering purposes. The value of the damage test correspondsto the maximum distance of etching into the imaged portion of thesilicon sample resulting from performing the damage test.

Ion microscope 200 can have a relatively large depth of focus. Forexample, in some embodiments, the depth of focus of ion microscope 200can be five nm or more (e.g., 10 nm or more, 100 nm or more, one μm ormore), and/or 200 μm or less (e.g., 100 μm or less, 10 μm or less). Insome embodiments, the depth of focus of ion microscope 200 can be from200 μm to five nm (e.g., from 500 μm to five nm, from one mm to fivenm). As used herein, the depth of focus of an ion beam is measured inthe following manner. A sample that includes gold islands formed on acarbon substrate (as discussed previously in connection with measurementof the He ion beam spot size) is inserted into the He ion microscope,and a measurement of the He ion beam spot size is performed as discussedabove. The location of the sample along the z-axis is iterativelyadjusted so that the position of the sample that yields the smallest Heion beam spot size is determined. This position along the z-axis isdenoted z_(f). The spot size of the He ion beam at z_(f) is denotedss_(f). The sample is then translated in increments along the −zdirection relative to z_(f). Spot size measurements of the He ion beamare performed (at the same location on the sample that was used todetermine z_(f)) after successive incremental translations. Translationof the sample is halted when the measured He ion beam spot size is2ss_(f). This position of the sample along the z-axis is denoted z_(u).Then, the sample is translated in increments along the +z directionrelative to z_(u), and through point z_(f). Spot size measurements ofthe He ion beam are performed (at the same location on the sample thatwas used to determine z_(f)) after successive incremental translations.Translation of the sample is halted when the measured He ion beam spotsize is 2ss_(f). This position of the sample along the z-axis is denotedz_(l). The depth of focus of the He ion microscope, d_(f), is calculatedas d_(f)=|z_(l)−z_(u)|.

In some embodiments, a gas field ion microscope (e.g., He ionmicroscope) as disclosed herein can be used to distinguish elements in asample having very close atomic numbers (Z values) using, for example,secondary electron yield, scattered ion abundance, and/or angle- andenergy-resolved scattered ion detection. For example, in certainembodiments, the gas field ion microscope can be used to distinguishelements having atomic numbers (Z values) that differ only by one.

In certain embodiments, a gas field ion microscope (e.g., He ionmicroscope) as disclosed herein can be used to distinguish elements in asample having a very close masses using, for example, secondary electronyield, scattered ion abundance, and/or angle- and energy-resolvedscattered ion detection. In certain embodiments, the gas field ionmicroscope can be used to distinguish elements having masses that differby one atomic mass unit or less (e.g., 0.9 atomic mass unit or less, 0.8atomic mass unit or less, 0.7 atomic mass unit or less, 0.6 atomic massunit or less, 0.5 atomic mass unit or less, 0.4 atomic mass unit orless, 0.3 atomic mass unit or less, 0.2 atomic mass unit or less, 0.1atomic mass unit or less). In some embodiments, a sample may havedomains formed of materials (e.g., alloys) having different averagemasses. In such embodiments, the gas field ion microscope can, forexample, be used to distinguish domains of material having masses thatdiffer only by one atomic mass unit or less (e.g., 0.9 atomic mass unitor less, 0.8 atomic mass unit or less, 0.7 atomic mass unit or less, 0.6atomic mass unit or less, 0.5 atomic mass unit or less, 0.4 atomic massunit or less, 0.3 atomic mass unit or less, 0.2 atomic mass unit orless, 0.1 atomic mass unit or less).

H. Optional Features

(i) High Efficiency Gas Use

In some embodiments, a more focused delivery of He gas to tip 206 canincrease the efficiency of He gas utilization within microscope system200. Typically, un-ionized He gas atoms can enter ion optics 130, whichcan increase the width of the distribution of energies of the ions inion beam 192. In addition, low energy un-ionized He gas atoms canparticipate in charge exchange interactions with high energy He ions,which can also increase the width of the energy distribution of ions inion beam 192.

Thus, in some embodiments, a gas delivery system can be designed toprovide gas (e.g., He gas) to tip 186 of gas field ion source 120 in amore targeted manner, and to remove unused gas (e.g., un-ionized He gas)from the system in a more efficient manner. For example, FIG. 21 is aschematic diagram of a portion of a gas field ion microscope thatincludes gas source 110 and a vacuum pump 734. Gas source 110 includes adelivery tube 730 of length q and diameter n terminating in a deliverynozzle 736, and vacuum pump 734 includes an inlet port 732. Nozzle 736is positioned at a distance g from apex 187 of tip 186, and inlet port732 is positioned at a distance l from apex 187 of tip 186.

In some embodiments, g can be 10 mm or less (e.g., 9 mm or less, 8 mm orless, 7 mm or less). Typically, g is 3 mm or more (e.g., 4 mm or more, 5mm or more, 6 mm or more). For example, g can be from 3 mm to 10 mm(e.g., from 4 mm to 9 mm, from 5 mm to 8 mm).

In certain embodiments, l can be 100 mm or less (e.g., 90 mm or less, 80mm or less, 70 mm or less, 60 mm or less, 50 mm or less). Typically, lis 10 mm or more (e.g., 20 mm or more, 30 mm or more, 40 mm or more).For example, l can be from 10 mm to 100 mm (e.g., from 30 mm to 100 mm,from 40 mm to 80 mm).

In some embodiments, the local pressure of He gas at the position ofapex 187 of tip 186 is 10⁻⁵ Torr or more (e.g., 10⁻⁴ Torr or more, 10⁻³Torr or more, 10⁻² Torr or more, 10⁻¹ Torr or more, 1 Torr or more). Atthe same time, the overall pressure of He gas in microscope system canbe reduced relative to systems that employ background introduction of Hegas. For example, the overall He pressure in microscope system 200 canbe 10⁻⁴ Torr or less (e.g., 10⁻⁵ Torr or less, 10⁻⁶ Torr or less, 10⁻⁷Torr or less, 10⁻⁸ Torr or less).

In some embodiments, the distance l and the cross-sectional area ofinlet port 732 are selected so that vacuum pump 734 captures unionizedHe atoms within a particular solid angle region of microscope system200. For example, for He atoms positioned at apex 187 of tip 186, thesolid angle subtended by inlet port 732 is 5° or more (e.g., 10° ormore, 15° or more, 20° or more, 30° or more, 40° or more).

In general, the ratio of the length q of delivery tube 730 to thediameter n of tube 730 can be selected to control the distribution oftrajectories of He gas atoms delivered to tip 186. For example, in someembodiments, the ratio q/n can be 3 or more (e.g., 4 or more, 5 or more,6 or more) and/or 10 or less (e.g., 9 or less, 8 or less, 7 or less). Incertain embodiments, the ratio q/n can be between 3 and 10 (e.g.,between 3 and 9, between 4 and 9, between 4 and 8, between 5 and 8,between 5 and 7).

In some embodiments, the gas delivery system can include more than onedelivery tube and nozzle. For example, in certain embodiments, the gasdelivery system can include two or more (e.g., three or more, four ormore, five or more, six or more) gas delivery tubes. Each of themultiple gas delivery tubes can be positioned to deliver He gas, in arelatively directed fashion, to tip 186. As a result of using multiplegas delivery tubes, the local pressure of He gas at the position of apex187 of tip 186 can be increased even further. One or more vacuum pumpscan be used to remove un-ionized He gas from microscope system 200.

In some embodiments, gas delivery tube 730 can be incorporated intoanother component of the system. For example, in certain embodiments,gas delivery tube 730 can be formed by one or more passageways (e.g.,two or more passageways, four or more passageways, six or morepassageways) for gas delivery in extractor 190 and/or suppressor 188. Insome embodiments, one or more passageways (e.g., two or morepassageways, four or more passageways, six or more passageways) for gasdelivery can be provided in posts which support tip 186 (e.g., posts 522a/b and 552). As an example, in certain embodiments, extractor 190 caninclude four passageways for gas delivery to tip 186. The passagewayscan be equally spaced and arranged radially along a circumference ofextractor 190 so that the opening of each passageway directly faces tip186. The length-to-diameter ratios of each of the passageways can be thesame, or different.

A number of advantages can be realized by incorporating gas deliverytubes into other elements of microscope system 200. For example, using ametal tube 730 placed close to tip 186 for gas delivery can perturbelectric fields in the vicinity of tip 186. Incorporation of the gasdelivery tube into another element of the microscope system caneliminate such perturbations. As another example, the spatial region inthe vicinity of tip 186 is typically crowded with electrodes and otherdevices for operation of microscope system 200. By incorporating gasdelivery tube 730 into another element of the system, crowding in thevicinity of tip 186 can be reduced.

In some embodiments, He gas delivered via delivery tube 730 can bepre-cooled so that it is near the operating temperature of tip 186 whenit enters microscope system 200. For example, a portion of delivery tube730 can be placed in contact with a supply reservoir of coolant (e.g.,liquid nitrogen) that is used to cool tip 186. As a result of thisthermal contact, He gas traveling through tube 730 is cooled toapproximately the same temperature as tip 186 before introduction intothe chamber where tip 186 is positioned.

(ii) Surface Charge Neutralization

In general, when He ions are incident on a surface of a sample,secondary electrons leave the sample. Many of the secondary electronsleave the sample, resulting in the surface having a net positive charge.Excess positive charges on the surface of the sample can produce anumber of undesirable effects. In some embodiments, the material of thesample can be damaged by the positive charges. For example, certainmaterials are charge sensitive, and can react violently (e.g., explode)in the presence of excess positive (or negative) charge.

In certain embodiments, positive charging of the surface of the samplecan limit the ability of detectors to detect secondary electrons thatleave the sample due to the interaction of the ion beam with the sample.For example, attractive forces between positive charges at the surfaceof the sample and the secondary electrons can decelerate the electrons,preventing the electrons from reaching a detector.

In some embodiments, positive charging of the surface of the sample cancause inaccurate ion beam rastering. Deflection and deceleration of theincident ion beam as a result of the electric field created by positivecharges at the surface of the sample can reduce the energy of theincident ions, and change their trajectories in difficult-to-predictfashion.

If the net positive charge on the surface of the sample becomes largeenough, the surface of the sample can act as an electrostatic mirror forHe ions, deflecting He ions away from the surface of the sample beforethe He ions reach the surface of the sample.

A flood gun capable of delivering a flux of electrons to the surface ofthe sample can be used to counteract surface charging effects. FIG. 22shows a portion of a gas field ion microscope that includes a flood gun840 configured to deliver an electron beam 842 to surface 181 of sample180 while He ion beam 192 is incident on surface 181. The electron fluxon surface 181 can, in general, be controlled so that surface chargingeffects are counterbalanced by electron beam 842 to the extent desired.

While FIG. 22 depicts ion beam 192 and electron beam 842 simultaneouslyimpinging on surface 181 of sample 180, other approaches may be used.For example, prior to exposing surface 181 to He ion beam 192, flood gun840 can be configured to deliver electron beam 842 to sample 180 tocreate a charge layer 846 in a sub-surface region of sample 180 (FIG.23). Layer 846 has an average depth m below surface 181, and layer 846has a thickness r measured in a direction normal to surface 181.Generally, the depth m and thickness r, as well as the density ofelectrons in layer 846, can be controlled by the energy of the electronsin electron beam 842, the angle of incidence of the electrons inelectron beam 842 with respect to surface 181, and the total dosage ofelectrons delivered to sample 180.

In some embodiments, when incident on surface 181, the average energy ofthe electrons in electron beam 842 is adjustable. For example, theaverage energy of the electrons can be 500 eV or more (e.g., 1 keV ormore, 2 keV or more), and/or 20 keV or less (e.g., 15 keV or less, 10keV or less). For example, when incident on surface 181, the averageenergy of the electrons in electron beam 842 can be from 500 eV to 20keV (e.g., from 1 keV to 15 keV, from 2 keV to 10 keV).

The angle of incidence δ of the electrons in electron beam 842 withrespect to surface 181 corresponds to the angle between a principaltrajectory 850 of electron beam 842 and a normal 848 to surface 181. Ingeneral, δ is 0° or more (e.g., 10° or more, 20° or more), and/or 80° orless (e.g., 70° or less, 60° or less). For example, δ can be from 0° to70° (e.g., from 0° to 10°, from 40° to 60°).

In certain embodiments, the total current of electrons delivered tosample 180 is 10 pA or more (e.g., 100 pA or more, 1 nA or more, 10 nAor more), and/or 100 μA or less (e.g., 10 μA or less, 1 μA or less, 500nA or less, 100 nA or less). For example, the total current of electronsdelivered to sample 180 can be from 10 pA to 1 μA (e.g., from 100 pA to100 nA, from 1 nA to 10 nA).

In some embodiments, m is 10 nm or more (e.g., 25 nm or more, 50 nm ormore, 75 nm or more, 100 nm or more), and/or 500 nm or less (e.g., 400nm or less, 300 nm or less, 200 nm). For example, m can be from 10 nm to500 nm (e.g., from 25 nm to 500 nm, from 50 nm to 500 nm, from 75 nm to400 nm, from 100 nm to 400 nm).

In certain embodiments, multiple flood guns can be used. For example, insome embodiments, different flood guns can be used to expose differentportions of surface 181 of sample 180 to electrons. In certainembodiments, each flood gun can be used to expose the same portion ofsurface 181 to electrons. Optionally, different flood guns can beoperated at different times. For example, one or more flood guns can beused to expose surface 181 to electrons before surface 181 is exposed toHe ions (e.g., to form a sub-surface charge layer), while one or moredifferent flood guns can be used to expose surface 181 to electronswhile surface 181 is also being exposed to He ions. In some embodiments,all the flood guns can be used to expose surface 181 to electrons beforesurface 181 is exposed to He ions (e.g., to form a sub-surface chargelayer), whereas in certain embodiments all the flood guns can be used toexpose surface 181 to electrons while surface 181 is also being exposedto He ions. Other combinations may also be used.

While embodiments have been described in which surface chargeneutralization can be achieved using a flood gun, surface chargeneutralization can also be achieved using a collector electrode tocollect ejected secondary electrons and return them to the surface ofthe sample to reduce the net positive charge at the surface. Referringto FIG. 24, a collector electrode 852 is connected to sample 180 viaconductor 854. When sample 180 is exposed to He ion beam 192, secondaryelectrons ejected from surface 181 of sample 180 (represented by arrow856) are incident on collector electrode 852. Electrons 856 are thenconveyed, via conductor 854, back to surface 181 to reduce the positivecharge at surface 181. Additional collector electrodes 852 can beconnected to sample 180 to provide for further surface chargeneutralization.

In certain embodiments, combinations of one or more collector electrodesand one or more flood guns can be used. For example, one or more floodguns can be used to expose surface 181 of sample 180 to electrons beforesurface 181 is exposed to He ions (e.g., to form a sub-surface chargelayer), and one or more collector electrodes can be used to neutralizecharging at surface 181 while surface 181 is being exposed to He ions.Other combinations are also possible.

In some embodiments, flood gun 840 can be configured to deliver a verylow energy beam of electrons 842 to sample 180. For example, electronsin beam 842 can have an average energy of about 50 eV or less. The lowenergy electrons have low landing energies, and this limits the amountof negative charge that can accumulate on surface 181. For example, ifthe average electron energy in electron beam 842 is 50 eV, once sample180 charges to a potential of −50 V relative to the common ground,electrons from flood gun 840 will no longer land on the surface of thesample. As a result, by adjusting the energy of the low energy electronsfrom flood gun 840, the maximum accumulated negative charge on surface181 of sample 180 can be controlled. This method can be used to imagenon-conducting materials without depositing a layer of conductivematerial on top of the non-conducting material to prevent charging ofthe non-conducting material. An example of this method is shown in FIG.25. Ion beam 192 is incident on surface 181 of sample 180, which is adielectric material with relatively low electrical conductivity (e.g.,sample 180 is not metallic). Sample 180 is supported by samplemanipulator 140, which is biased at an electrical potential of −600 Vrelative to the common external ground of microscope system 200. Theelectrical potential applied to manipulator 140 creates an electricfield at surface 181 of sample 180. Flood gun 840 is configured todeliver an electron beam that includes electrons having an averageenergy of 500 eV to surface 181 in the vicinity of the impinging ionbeam 192. Initially, the electric field at surface 181 due to the biasapplied to manipulator 140 causes deflection of the electrons from floodgun 840 along trajectories such as 843 a and 843 b—the electrons do notland on surface 181. However, as positive charge accumulates on surface181 due to the incident He ions, sample 180 becomes positively-charged,reducing the electric field strength experienced by electrons from floodgun 840. When the charge on surface 181 of sample 180 accumulates to thepoint where the effective bias at the surface reaches −500 V relative tothe common ground, electrons from flood gun 840 can land on surface 181and neutralize positive charges thereon, following trajectories such as843 c, for example. As a result, by controlling the bias applied tomanipulator 140 and the energy of the electrons delivered by flood gun840, positive charge accumulation on sample 180 can be controlled.Sample 180, a non-conducting material, can thus be imaged without theaccumulation of surface charge, which might otherwise lead toundesirable image contrast due to voltage contrast effects that resultfrom surface charging. Images of non-conducting and semiconductingmaterials can be obtained without depositing a layer of conductivematerial on the sample to act as a charge dissipation layer.

In some embodiments, flood gun 840 can be configured to deliverelectrons to sample 180 which have a negative landing energy—that is, inthe absence of positive charge on the sample surface, electrons that donot land at all on surface 181. When sample 180 acquires surface chargedue to incident He ions, electrons from flood gun 840 begin to land onsurface 181, neutralizing the positive charge. As a result, surface 181of sample 180 is maintained in an approximately uncharged state.

In some embodiments, a conversion surface can be used to generatesecondary electrons, which can then be used to neutralize positivecharges that accumulate at surface 181 of sample 180. For example, aconversion surface formed of a material with a high secondary electronyield (e.g., platinum) can be positioned in proximity to sample 180.High energy He ions and/or neutral atoms, leaving sample 180, can strikethe conversion surface, generating secondary electrons. The generatedsecondary electrons experience attractive forces due to accumulatedpositive surface charge on sample 180. As a result, the secondaryelectrons land on the sample surface, neutralizing the positive chargesand reducing the electric field due to surface charge. Consequently,secondary electrons are attracted more strongly to surface 181 of sample180 when there is a greater accumulation of surface positive charge.This provides a self-regulating mechanism for reducing surface charging.

In some embodiments, a conversion plate can be mounted directly to anelement of ion optics 130 to provide secondary electrons for surfacecharge neutralization of sample 180. For example, in FIG. 26, aconversion plate 845 is attached to a surface of second lens 226.Electrons 842 from flood gun 840 are directed to be incident on theconversion plate, which is formed from a material with a high secondaryelectron yield. He ion beam 192 is incident on surface 181 of sample 180and, over time, positive charge accumulates on surface 181 in the regionwhere ion beam 192 is incident. Secondary electrons 847, generated fromconversion plate 845, are attracted to surface regions with excesspositive charge and land on these regions, neutralizing excess positivecharge. Once the excess surface charge is eliminated, further secondaryelectrons do not land on surface 181. As a result, surface 181 can bemaintained in a quasi-neutral state.

In general, flood gun 840 can be configured for either continuous orintermittent operation. In particular, during intermittent operation,flood gun 840 can be turned on and off at a desired rate. For example,in some embodiments, flood gun 840 can be turned on and off to providecharge neutralization of sample 180 at a pixel exposure rate. Ion beam192 can be rastered across the surface of sample 180 in discrete stepsto expose successive portions of the sample surface. After each portionis exposed, flood gun 840 can be used to neutralize surface charge inthe exposed region. This corresponds to charge neutralization at a pixelexposure rate. Alternatively, or in addition, flood gun 840 can be usedto perform neutralization at a line scan rate (e.g., after an entireline of discrete portions of sample 180 have been exposed to ion beam192), and/or at a frame rate (e.g., after an entire two-dimensional areaof discrete portions of sample 180 have been exposed to ion beam 192).

In some embodiments, flood gun 840 can be used to improve the ease ofdetection of secondary electrons from sample 180. For example, flood gun840 can be used to embed a layer of charge (e.g., charge layer 846)within a bulk region of sample 180. The embedded layer of negativecharge induces an electric field at surface 181 of sample 180. Secondaryelectrons that leave sample 180 due to the interaction of sample 180with the incident ion beam 192 are accelerated away from sample 180 dueto the electric field created by charge layer 846, making detection ofthe secondary electrons by a suitably configured detector relativelyeasier.

An example of the use of an embedded layer of negative charge is shownschematically in FIGS. 27A and 27B. In FIG. 27A, ion beam 192 isincident on surface 181 of sample 180. A plurality of secondaryelectrons 2012 are generated within the first few nanometers of sample180. At first, many of the secondary electrons escape as free electrons2014, which can be detected by a suitably configured detector. Overtime, however, incident He ions implant within sample 180, forming apositively-charged layer 2010 within sample 180. As the net positivecharge within layer 2010 increases, secondary electrons 2012 areincreasingly attracted toward layer 2010, and fewer and fewer secondaryelectrons 2012 escape sample 180 as free electrons 2014. As a result,imaging of sample 180 via detection of secondary electrons can becomeincreasingly difficult.

A solution to this problem is shown in FIG. 27B. In the embodiment shownin FIG. 27B, flood gun 840 (not shown) is used to embed a layer ofnegative charge 2016 (e.g., electrons) within sample 180. The embeddedlayer of negative charge is similar to layer 846 in FIG. 23. As a resultof layer 2016, secondary electrons 2012 generated in sample 180 areaccelerated away from sample 180, resulting in an increase in the numberof generated secondary electrons 2014 that escape sample 180, andtherefore enhancing the detected secondary electron signal from thesample. In effect, layer 2016 acts as an electrostatic mirror forsecondary electrons, enhancing their detectability.

In general, flood gun 840 can be used to implant electrons in a sampleprior to the analysis of the sample, and/or flood gun 840 can be used toimplant electrons in a sample while imaging the sample. In someembodiments, the sample may be exposed to electrons from flood gun 840at intervals (e.g., regular intervals). This can, for example, assist inmaintaining a relatively consistent level of charging. For example, thesample may be exposed to electrons from flood gun 840 at time periodscorresponding to a dwell time per pixel (e.g., 100 ns).

(iii) Vibration Decoupling

Mechanical vibrations due to vacuum pumps, various moving parts, andbackground acoustic disturbances can affect certain performanceparameters (e.g., imaging resolution, ion beam spot size at sample 180,stability) of a gas field ion microscope system 200. In someembodiments, sample manipulator 140 can be configured to decouple sample180 from other parts of system 200, thereby reducing the impact ofexternal mechanical disturbances. FIG. 28 shows a vibration-decoupledsample manipulator 140 that includes a guiding needle 906 supported byan actuator 908, with needle 906 and actuator 908 each located within astage 904. A support disk 902 is positioned atop stage 904, and afriction spider 900, which supports sample 180, is placed atop disk 902.

To move sample 180 in the x-y plane, actuator 908 receives a suitablesignal from electronic control system 170 and actuates guiding needle906. Guiding needle 906 nudges sample 180 and/or spider 900, causingtranslation in the x-y plane, in response to signals from actuator 908.

A width j of guiding needle 906 at its apex is typically chosen to beslightly smaller than a diameter b of aperture 910 in spider 900. Forexample, j can be 1 mm, and b can be 1.1 mm. In addition, spider 900 anddisk 902 are selected such that the static frictional force between disk902 and spider 900 is large, but can be overcome by the force applied byactuator 908 to sample 180 through guiding needle 906. Guiding needle906 is formed of a mechanically compliant material that can deform underan applied stress to reduce transmission of vibrations to sample 180,but is stiff enough to transmit to sample 180 the force applied byactuator 908.

As a result of these system parameters, mechanical vibrations that arecoupled into stage 904 can be partially absorbed and dissipated byguiding needle 906 so that there is little or no vibration of spider900. Additionally, if guiding needle 906 does apply a force to spider900, guiding needle 906 will preferentially slip against the sides ofspider 900, rather than induce vibration of spider 900.

In some embodiments, guiding needle 906 can have a substantiallyrectangular cross-sectional shape. A rectangular cross-sectional shapemay assist in ensuring that rotation of sample 180 and/or of spider 900does not occur as spider 900 is translated in the x- and/or y-directionsby guiding needle 906. If sample manipulator 140 is tilted with respectto axis 132 of ion optics 130 (e.g., so that ion beam 192 is incidentupon sample 180 at a non-normal angle), the materials used to formspider 900 and/or disk 902 can be selected so that an even higher staticfrictional force between these elements is present. Alternatively, or inaddition, in certain embodiments, spider 900 and disk 902 can bemagnetically coupled to increase the frictional force between theseelements. Magnetic field coupling can be carefully implemented to ensurethat the magnetic field is localized and does not disturb sample 180 orimpinging ion beam 192.

Guiding needle 906 can be completely disengaged from spider 900 whenneedle 906 is not actuated. For example, after guiding needle 906 hasapplied a force to spider 900 causing spider 900 and sample 180 to betranslated in the x-y plane, a small recoil motion of needle 906 can beinduced by electronic control system 170, which introduces a spacebetween guiding needle 906 and spider 900. As a result, guiding needle906 is completely disengaged from spider 900, and coupling of mechanicalvibrations to spider 900 via needle 906 are prevented.

FIG. 29 depicts a sample holder assembly 1510 for a microscope system.Sample holder assembly 1510 reduces the use of bearings and helps reducelow frequency mechanical vibrations in the sample during operation.Assembly 1510 includes a body 1511 having an opening 1512 to insert asample. Body 1511 is connected to arms 1518 through adjustableconnectors 1522. Arms 1518 support a sample stage 1514 using grips 1520.Sample stage 1514 includes a surface disk 1516 having an aperture 1524.

Assembly 1510 may be connected to an ion microscope such that tip 186 ispointed towards aperture 1524 on sample stage 1514. Body 1511 may beformed from suitable rigid materials such as hardened steel, stainlesssteel, phosphor bronze, and titanium. Body 1511 may be sized and shapedto suit the particular needs of the application. As an example, the sizeand shape of body 1511 may be chosen for use with the microscope systemsdisclosed herein. During operation, a sample may be introduced toassembly 1510 through opening 1512.

Sample stage 1514 is supported by arms 1518 connected to body 1511 alongadjustable connectors 1522. Adjustable connectors 1522 allow forvertical movement of arms 1518. Arms 1518 and sample stage 1514 can bemoved in a vertical direction and locked in a specific position.Connectors 1522 can be pneumatic or vacuum controlled such that arms1518 and stage 1514 can be tightly locked in a desired verticalposition. Connectors 1522 can optionally include other types ofconnectors.

Sample stage 1514 is connected to arms 1518 using grip 1520. Arm 1518can have a shaft extending inwards such that grip 1520 of sample stage1514 can clasp the shaft. Grip 1520 can be pneumatically or vacuumoperated such that stage 1514 can be tilted. Grip 1520 can be controlledsuch that stage 1514 is tilted to a desired position. In someembodiments, after a desired position has been reached, grip 520 can betightened such that sample stage 1514 is tightly locked in the desiredtilted position.

Sample stage 1514 further includes surface disk 1516 having an opening1524. A sample may be placed on disk 1516 and a sample position controlsystem can be introduced through opening 1524 to move the sample on theplane of disk 1516. In certain embodiments, disk 1516 can be rotatedabout its center to rotate and move the sample located on the surface ofthe disk as desired. Disk 1516 may be formed from suitable rigidmaterials including ceramic, glass and polymers.

FIG. 30 depicts a sample holder assembly for a microscope system. Thesample holder assembly of FIG. 30 is similar to the sample holderassembly of FIG. 29 with a spider 1600 placed on a surface of disk 1516.Spider 1600 can have legs to allow it to be positioned on top of opening1524. Optionally, spider 1600 can have an opening on a portion of thesurface. Spider 1600 can be formed from suitable rigid materialsincluding ceramic, glass and polymers.

During operation of microscope system 200, sample 180 can be moved inthe z-direction, tilted, translated in the x-y plane, and rotated. Ifsample 180 is tilted and the tilt angle (e.g., the angle between ionbeam 192 and a normal to the surface of sample 180) is relatively large,the inclined sample may not be in focus over the entire field of view ofmicroscope system 200. As a result, the image of the sample obtainedunder these conditions may be out of focus and blurred at the areasoutside of the center and vertical to the tilt axis.

These can be compensated by changing the focal length of lens 226 as ionbeam 192 is scanned over the surface of sample 180. To perform thiscorrection, sample manipulator 140 can transmit tilt angle informationfor sample 180 to electronic control system 170. Alternatively, tiltangle information can be entered manually by a system operator via auser interface. Electronic control system 170 can determine, based uponthe orientation of sample 180, a set of voltage corrections to apply tosecond lens 226 to dynamically change the focal length of lens 226 asion beam 192 is scanned over the surface of tilted sample 180.

In addition, the lateral dimensions of the inclined sample are distorteddue to the projection of the tilted sample on a plane surface and due tothe difference in distance to the ion optics 130. For example, lateraldimensions of inclined sample surfaces may appear shorter that theyactually are due to the orientation of sample 180 with respect to ionbeam 192. Another example is the keystone distortion of the image. Theeffect is that a rectangular feature is distorted so that the image ofthe rectangle appears to be keystone in its shape.

These can be compensated by adjusting the scan amplitude of scanningdeflectors 219 and 221 as ion beam 192 is scanned over the surface ofsample 180. To perform this correction, the electronic control system170 can get the information about the tilt angle for sample 180 in thesame way as described above. Electronic control system 170 candetermine, based upon the tilt of sample 180, adjustments of the scanamplitude to apply to scanning deflectors 219 and 221 to adapt the ionbeam deflection as ion beam 192 is scanned over the surface of tiltedsample 180 for an undistorted imaging of the surface of tilted sample180. Alternatively, these two distortion effects can be corrected bydigital manipulation of the distorted image.

(iv) Reducing the Presence of Neutral Particles and Doubly-Charged Ionsin the Ion Beam

As discussed above, neutral particles (e.g., He atoms) can enter ionoptics 130 of microscope system 200 as un-ionized neutral atoms from gasfield ion source 120. Such neutral particles can negatively impact theperformance of the microscope system. Therefore, in some embodiments, itis desirable to reduce the presence of neutral particles in ion beam192. Doubly-charged He ions (e.g., He²⁺) can also be produced in gasfield ion source 120, either via double-ionization of He atoms in thevicinity of tip 186, or by collisions between He ions. The focusingproperties of doubly-charged He ions are different from singly-chargedions, and doubly-charged ions present in ion beam 192 can lead to largerspot sizes on sample 180 and other undesirable effects.

One approach to reducing the population of neutral particles in ion beam192 involves reducing the probability that neutral particles will maketheir way into the ion beam. Such an approach can involve, for example,using directed gas delivery to tip 186 (see discussion above) to reducethe overall presence of un-ionized He gas atoms in microscope system200.

Another approach to reducing the population of neutral particles in ionbeam 192 involves removing neutral particles from the ion beam after theneutral particles are present in ion beam 192. This approach can involvethe use of electrostatic lens elements to deflect ions, spatiallyseparating ions and neutrals in ion optics 130. For example, FIG. 31shows ion optics 130 in which deflector 220 is offset from longitudinalaxis 132 of ion optics 130, and in which an additional deflector 223 isdisposed. He ion beam 192 includes He ions 192 a and He atoms 192 b. Toseparate He ions 192 a and He atoms 192 b, the electrical potentialapplied to deflector 223 is adjusted to cause deflection of He ions 192a in the x-direction. He atoms 192 b are unaffected by deflector 223,and are therefore undeflected. He atoms 192 b are subsequentlyintercepted by collector 1016, which prevents He atoms 192 b frompassing through aperture 224. The electrical potentials applied todeflectors 220 and 222 are also adjusted so that the trajectories of Heions 192 a are re-aligned with longitudinal axis 132, and a portion ofHe ions 192 a pass through aperture 224 and are incident on surface 181of sample 180 as ion beam 192.

Other techniques may also be used to remove neutral particles from anion beam. Typically, such techniques involve deflecting the ions in theion beam using electric and/or magnetic field(s), without deflecting theneutral particles. In some embodiments, combinations of electric andmagnetic fields can be used to compensate for energy dependent spatialseparation of ions resulting from ion deflection in ion optics 130. Inaddition, various asymmetric ion column geometries (e.g., bent ioncolumns) can be used to separate He atoms and ions.

For example, in FIG. 32, a bent column configuration of ion optics 130can be used to separate He atoms, singly-charged He ions, anddoubly-charged He ions. Ion beam 192 enters ion optics 130 propagatingalong a direction that is tilted with respect to axis 132 of ion optics130. Ion beam 192 includes neutral He atoms, He⁺ ions, and He²⁺ ions. Anelectrical potential is applied to deflector 223, deflecting He⁺ ions inion beam 192 so that after passing through deflector 223, the He⁺ ionspropagate along axis 132 as ion beam 192 a. However, neutral atoms areundeflected on passing through deflector 223. The neutral atoms aretherefore spatially separated from He⁺ ions, providing a neutral atombeam 192 b which is intercepted by collector 1016 b. He²⁺ ions aredeflected to an even greater extent than He⁺ ions, spatially separatingsingly- and doubly-charged ions, and providing an ion beam 192 c of He²⁺ions. The He²⁺ ion beam 192 c is intercepted by collector 1016 c. As aresult, ion beam 192 a which emerges from ion optics 130 includessubstantially only He⁺ ions.

FIG. 33 shows another embodiment of an ion optical system for separatingHe atoms, He⁺ ions, and He²⁺ ions. The ion optical system shown in FIG.33 includes a dispersionless sequence of electric and magnetic fieldswhich are used to isolate He atoms, He⁺ ions, and He²⁺ ions from oneanother, and which do not contribute prism-like effects to the particlebeams. The ion optical system includes a series of three deflectors 223a, 223 b, and 223 c, which are configured to deflect and direct He⁺ ionsthrough ion optics 130 so that ion beam 192 a, which includessubstantially only He⁺ ions, emerges from ion optics 130. Neutral atombeams 192 b are undeflected and are intercepted at positions followingeach deflector by collectors 1016 b. Doubly-charged He ions aredeflected even further than He⁺ ions, and multiple He²⁺ beams 192 c areintercepted by collectors 1016 c. As a result, He atoms, He⁺ ions, andHe²⁺ ions are spatially separated from one another, and the He⁺ ions aredirected toward sample 180 as ion beam 192, while the undesired beamconstituents are blocked in ion optics 130.

In some embodiments, the use of magnetic fields can lead to spatialseparation of the trajectories of ions in ion beam 192 which have thesame charge, but which correspond to different isotopes of the gasintroduced by gas source 110. For certain gases such as He, which have adominant naturally occurring isotope (e.g., greater than 90% relativeabundance), separation effects due to magnetic fields are typicallysmall. However, for other gases which have two or more naturallyoccurring isotopes and which lack a dominant isotope, such effects canbe greater. As a result, in certain embodiments, an isotope separator(e.g., a block used to prevent undesired isotopes from traversing thelength of ion optics 130) can be used. In some embodiments, a collector1016 that is used to block neutral atoms or doubly-charged ions can alsobe used to block unwanted isotopes in ion beam 192.

Types of Particles

The interaction of the ion beam with the sample can cause differenttypes of particles to leave the surface through various interactions asdescribed below. Such particles include secondary electrons, Augerelectrons, scattered ions, primary neutral particles, X-ray photons, IRphotons, visible photons, UV photons, secondary ions and secondaryneutral particles. One or more types of particles can be detected andanalyzed to determine one or more different types of information aboutthe sample. Such types of information about the sample includetopographical information about the surface of the sample, materialconstituent information about the surface of the sample, materialconstituent information about a sub-surface region of the sample,crystalline information about the sample, voltage contrast informationabout the surface of the sample, voltage contrast information about asub-surface region of the sample, magnetic information about the sample,and optical information about the sample. As used herein, the termsurface of a sample refers to the volume up to a depth of five nm orless.

A. Secondary Electrons

A secondary electron, as referred to herein, is an electron that isemitted from a sample species and that has an energy of less that 50 eV.In general, secondary electrons are emitted from the sample surface at arange of angles and energies. However, the information of most interestis usually the total abundance of secondary electrons (as opposed toenergy-resolved secondary electron information, or angle-resolvedsecondary electron information) because, as explained below, the totalabundance of the secondary electrons is what can provide informationregarding the sample surface.

Secondary electrons can be detected using one or more appropriatedetectors capable of detecting electrons (see discussion above regardingtypes of detectors). If multiple detectors are used, the detectors mayall be the same type of detector, or different types of detectors may beused, and may generally be configured as desired. The detectors can beconfigured to detect secondary electrons leaving surface 181 of sample180 (the surface on which the ion beam impinges), surface 183 of sample180 (the surface on the opposite side from where the ion beam impinges)or both (see discussion above regarding configurations of detectors).

Detected secondary electron signals can be used to form an image of asample. Generally, the ion beam is raster-scanned over a field of viewof the surface of the sample, and the secondary electron signal at eachraster step (which corresponds to an individual pixel in an image) ismeasured by one or more detectors. Usually, each detector remains infixed position relative to the sample as the ion beam is raster-scannedover the field of view of the surface of the sample. In certainembodiments, however, one or more detectors can be moved relative to thesample. For example, if a single detector is being used, moving thedetector relative to the sample can yield angle-dependent informationabout the sample.

In certain embodiments, detecting the total abundance of secondaryelectrons can provide information regarding the topography of a sample.The secondary electron total abundance at a given location on a surfacegenerally depends upon the slope of the surface relative to the ion beamat that point. In general, the secondary electron total abundance ishigher where the slope of the surface relative to the ion beam is higher(i.e., where the angle of incidence of the ion beam as measured from thesurface normal is larger). Thus, the change in the total abundance ofsecondary electrons as a function of the location of the ion beam on thesurface of the sample, can be correlated to a change in the slope of thesurface, providing information regarding the topography of the surfaceof the sample.

In some embodiments, detecting the total abundance of secondaryelectrons can yield material constituent information (e.g., elementalinformation, chemical environment information) about a sample. In suchembodiments, the information is predominantly related to the surface ofthe sample. In general, each element or material in a given chemicalenvironment will have a particular inherent secondary electron yield. Asa result, the secondary electron total abundance at a given location ona surface generally depends on the material present at that location.Therefore, the change in the total abundance of secondary electrons as afunction of the location of the ion beam on the surface of the sample,can be correlated to a change in the element(s) and/or material(s)present at the surface of the sample, providing material constituentinformation about the surface of the sample. In certain embodiments,specific materials in a sample can be identified based on quantitativemeasurements of secondary electron yields from the sample. For example,materials such as Al, Si, Ti, Fe, Ni, Pt, and Au have known secondaryelectron yields when exposed to a He ion beam under controlledconditions. An ion microscope (e.g., a gas field ion microscope) can becalibrated based on known secondary electron yields for variousmaterials to identify the presence and relative abundance of a varietyof different materials in a sample under study. For example, secondaryelectron yields for various materials are shown in Table I. The yieldswere measured at normal incidence of the He ion beam, and at an averageion energy of 21 keV. At non-normal angles of incidence, for example,the yields shown in Table I are typically scaled by a multiplicativefactor that corresponds to the secant of the angle of incidence of theion beam on the surface of the sample. Other experimental conditions aredescribed in the corresponding Example noted below. TABLE I Material Z M(amu) Yield of secondary electrons Aluminum 13 27.0 4.31 Silicon 14 28.12.38 Titanium 22 47.9 3.65 Iron 26 55.8 3.55 Nickel 28 58.7 4.14 Copper29 63.4 3.23 Indium 49 114.8 4.69 Tungsten 74 183.8 2.69 Rhenium 75186.2 2.61 Platinum 78 195.1 7.85 Gold 79 197.0 4.17 Lead 82 207.2 4.57

In certain embodiments, detecting the total abundance of secondaryelectrons can yield voltage contrast information, which in turn, canprovide information regarding the electrical conductivity propertiesand/or the electrical potential of an element and/or a material at thesurface of a sample. The secondary electron total abundance at a givenlocation on the surface of a sample usually depends on the electricalproperties of the material present at the surface of the sample. Ingeneral, less electrically conducting materials will tend to becomepositively charged over time while being exposed to an ion beam overtime, whereas more electrically conducting materials will have less of atendency to become positively charged over time while being exposed toan ion beam. Hence, for example, the secondary electron total abundanceat a given location of the surface of a sample will tend to decreaseover time for a material that is less electrically conducting (due tomore surface charging resulting in fewer secondary electrons escapingthe sample), while the secondary electron total abundance at a givenlocation of the surface of the sample that is more electricallyconducting will tend to undergo less reduction in secondary electrontotal abundance over time (due to less surface charging). As a result,the change in the total abundance of secondary electrons as a functionof the ion beam location at the sample surface can be correlated to theelectrical conductivity of the material at that location, providingvoltage contrast information about the surface of the sample.

Sub-surface voltage contrast effects can be provided by He ions whichbecome embedded within sub-surface regions of the sample. As describedin connection with FIGS. 27A and 27B, sub-surface He ions can preventsecondary electrons generated in the sample from escaping the samplesurface. Thus, contrast in secondary electron images of the sample canbe due to sub-surface charging of the sample by incident He ions.

The information provided by these techniques can be used for ion beamtesting of semiconductor articles. For example, voltage contrastmeasurements can be used to determine whether portions of electricaldevices and/or circuits are at different potentials when exposed to theion beam due to the presence or absence of electrical connectionsbetween the portions, and therefore whether the devices and/or circuitsare operating correctly or not.

In some embodiments, detecting the total abundance of secondaryelectrons can provide crystalline information about a sample. The totalabundance of secondary electrons can vary depending on whether the ionbeam is aligned with the crystal structure of the sample (e.g., alignedparallel to one of the unit vectors describing the crystal lattice) ornot. If the ion beam is aligned with the crystal structure of thesample, the probability that ions in the ion beam can generallypenetrate into a given distance into the sample without undergoing acollision with a sample atom (commonly referred to as channeling) isrelatively high, resulting in a lower total abundance of secondaryelectrons. If, on the other hand, the ion beam is not aligned with thecrystal structure, then the ions in the ion beam will have a lowerprobability of penetrating into the sample the given distance withoutundergoing a collision with a sample atom, resulting in a higher totalabundance of secondary electrons. Therefore, the change in the totalabundance of secondary electrons as a function of the ion beam locationat the sample surface can be correlated to the crystalline informationof the material at that location. For example, there may be regions ofthe sample surface where the secondary electron total abundance issubstantially the same. Such regions can, for example, have the samecrystal orientation, and the size of the regions can provide grain sizeand/or crystal size information (e.g., in a polycrystalline sample thatincludes multiple, oriented crystal domains), and/or can provideinformation regarding strained regions of sample (whether amorphous orcrystalline) because the magnitude of the secondary electron totalabundance for a material of a given chemical composition (e.g.,elemental composition, material composition) can depend on the strain ofthe material.

In certain embodiments, detecting the total abundance of secondaryelectrons can provide magnetic information about a sample. The totalabundance of secondary electrons can depend on the magnitude of amagnetic field adjacent the sample surface. In some embodiments, forexample, the magnetic field adjacent to the sample surface varies due tomagnetic domains within the sample that produce local magnetic fields atthe sample surface. In certain embodiments, a static magnetic field isapplied by an external magnetic field source, and magnetic domainswithin the sample produce local magnetic fields at the surface of thesample that introduce variations in the applied external magnetic field.In either case, variations in the local magnetic field at the surface ofthe sample can, for example, change the trajectories of secondaryelectrons ejected from the sample. The change in secondary electrontrajectories can correspond to an increase in the total abundance ofsecondary electrons when the trajectories of the secondary electrons arechanged so that more secondary electrons are directed toward thedetector(s), or the change in secondary electron trajectories cancorrespond to a decrease in the total abundance of secondary electronswhen the trajectories of the secondary electrons are changed so thatmore secondary electrons are directed away from the detector(s).

For some samples, the contrast that appears in a secondary electronimage of the sample may be due to two or more of the mechanismsdiscussed above. In other words, secondary electron images of certainsamples can include contrast that is due in part to topographicvariations in the sample surface, material constituent variations in thesample surface, voltage contrast variations in the sample surface,crystalline variations in the sample surface, and/or magnetic variationsin the sample surface. Accordingly, it can be advantageous to combineinformation gained from measuring the secondary electron total abundancewith information gained from measuring other types of particles toqualitatively and/or quantitatively isolate contributions from one ormore of these mechanisms. This possibility is discussed in more detailbelow.

Secondary electron imaging techniques can be applied to a variety ofdifferent classes of samples. An example of such a class of materials issemiconductor articles, such as patterned wafers, which can include, forexample, multiple electrical conductors surrounded by a matrix ofinsulating material. Secondary electron imaging techniques can be usedto identify defects in the device, such as incomplete electricalconnections between conductors, and/or electrical shorts between circuitelements. More generally, secondary electron imaging techniques can beused for a wide range of ion beam testing applications of semiconductorarticles. Optionally, this approach can similarly be used for purposesof mask repair.

Another example of a sample class for which secondary electron imagingtechniques can be used is metals and alloys. For example, images ofsamples that contain mixed materials such as alloys can be used todetermine the surface distribution of each of the materials in thesample. Yet another example of a sample class where secondary electronimaging techniques can be used is read/write structures for datastorage. Additional examples of classes of materials for which secondaryelectron imaging techniques can be used are biological materials andpharmaceutical materials.

Imaging samples using secondary electrons generated by exposure to a Heion beam can provide a number of advantages relative to secondaryelectron imaging via other techniques, such as SEM. For example, thespot size of the He ion beam on the sample can be smaller than the spotsize of an electron beam from a SEM. As a result of the smaller spotsize, the region of the sample that is exposed to the He ion beam ismore carefully controlled than the exposed region in a SEM.

Further, in general, because He ions are heavier than electrons,scattering events do not disperse He ions as readily within the sampleas electrons are dispersed by scattering. As a result, He ions incidenton the surface of a sample can interact with the sample in a smallerinteraction volume than electrons in a SEM. As a result, secondaryelectrons detected in a gas field ion microscope (e.g., a He ionmicroscope) can arise from a smaller region than the region giving riseto secondary electrons in a SEM with a similar spot size. Consequently,the secondary electrons which are generated by the He ion beam cancorrespond to a more localized interrogation of the surface of thesample (e.g., with less lateral averaging of material properties) thanthe secondary electrons generated in a SEM.

In addition, the He ion source also provides a greater depth of focusthan an electron source. As a result, images of a sample obtained usingan ion microscope (e.g., a gas field ion microscope) can show a largerportion of the sample, measured along the direction perpendicular to thesample surface, in focus than comparable images obtained from secondaryelectrons in a SEM.

He ion beams can also provide a more sensitive contrast mechanism forsecondary electron images of a sample due to a larger range of secondaryelectron yields for different materials available when causing thesecondary electrons to leave the sample due to the interaction of theion beam with the sample, as compared to when causing the secondaryelectrons to leave the surface due to the interaction of an electronbeam with the sample. Typically, for example, secondary electron yieldsfor common materials such as semiconductors and metals vary from 0.5 to2.5 for an incident electron beam. However, secondary electron yieldsfor the same materials exposed to a He ion beam can vary from 0.5 to 8.Thus, identification of different materials from secondary electronimages can be performed more accurately using a gas field ion microscope(e.g., a He ion microscope) than in comparable SEM systems.

B. Auger Electrons

As referred to herein, an Auger electron is an electron generated asfollows. An inner shell atomic electron is removed to form a vacancy,followed by filling of the vacancy by a second atomic electron from ahigher shell with the release of energy. This energy is released viaanother electron called an Auger electron. In general, Auger electronsare emitted from the sample surface at a range of angles and energies.However, the information of most interest is usually the energy of theAuger electrons (as opposed to angle-resolved Auger electroninformation) because, as explained below, the energy of the Augerelectrons is what can provide information regarding the sample surface.Auger electrons can be detected using one or more appropriate detectorscapable of detecting electrons in an energy-resolved fashion (seediscussion above regarding types of detectors). If multiple detectorsare used, the detectors may all be the same type of detector, ordifferent types of detectors may be used, and may generally beconfigured as desired. The detectors can be configured to detect Augerelectrons leaving surface 181 of sample 180 (the surface on which theion beam impinges), surface 183 of sample 180 (the surface on theopposite side from where the ion beam impinges) or both (see discussionabove regarding configurations of detectors). To enhance the signal tonoise of the detected Auger electrons, it can be desirable to use adetector that can collect a relatively large solid angle of Augerelectrons. Additionally or alternatively, electron collection optics(e.g., an electrostatic lens system) that are adjacent the surface ofthe sample and that can direct the electrons to the detector can be used(e.g., to increase the effective solid angle of detection for the Augerelectrons).

In general, detecting the energy of Auger electrons can yield materialconstituent information (e.g., elemental information, chemicalenvironment information) about a sample. In such embodiments, theinformation is predominantly related to the surface of the sample. Ingeneral, for each element or material in a given chemical environment,the Auger electrons emitted by the element or material will have aparticular energy or band of energies. As a result, the energy of theAuger electrons at a given location on a surface generally depends onthe material present at that location. Therefore, the change in theenergy of the Auger electrons as a function of the location of the ionbeam on the surface of the sample, can be correlated to a change in theelement(s) and/or material(s) present at the surface of the sample,providing material constituent information about the surface of thesample.

Auger electron imaging techniques can be applied to a variety ofdifferent classes of samples. An example of such a class of materials issemiconductor articles, such as patterned wafers, which can include, forexample, multiple electrical conductors surrounded by a matrix ofinsulating material. Optionally, this approach can similarly be used forpurposes of mask repair. Another example of a sample class for whichAuger electron imaging techniques can be used is metals and alloys. Forexample, images of samples that contain mixed materials such as alloyscan be used to determine the surface distribution of each of thematerials in the sample. Yet another example of a sample class whereAuger electron imaging techniques can be used is read/write structuresfor data storage. Additional examples of classes of materials for whichAuger electron imaging techniques can be used are biological materialsand pharmaceutical materials.

Imaging samples using Auger electrons that leave the surface due to theinteraction of the sample and the He ion beam can provide a number ofadvantages relative to Auger electron imaging via other techniques, suchas SEM. For example, the spot size of the He ion beam on the sample canbe smaller than the spot size of an electron beam from a SEM. As aresult of the smaller spot size, the region of the sample that isexposed to the He ion beam is more carefully controlled than the exposedregion in a SEM.

Further, in general, because He ions are heavier than electrons,scattering events do not disperse He ions as readily within the sampleas electrons are dispersed by scattering. As a result, He ions incidenton the surface of a sample can interact with the sample in a smallerinteraction volume than electrons in a SEM. As a result, Auger electronsdetected in a gas field ion microscope (e.g., a He ion microscope) canarise from a smaller region than the region giving rise to Augerelectrons in a SEM with a similar spot size. Consequently, the Augerelectrons which leave the surface due to the interaction of the sampleand the He ion beam can correspond to a more localized interrogation ofthe surface of the sample (e.g., with less lateral averaging of materialproperties) than the Auger electrons generated in a SEM.

In addition, the He ion source also provides a greater depth of focusthan an electron source. As a result, images of a sample obtained usingan ion microscope (e.g., a gas field ion microscope) can show a largerportion of the sample, measured along the direction perpendicular to thesample surface, in focus than comparable images obtained from Augerelectrons in a SEM.

Another advantage of using an ion beam, as opposed to an electron beam,for Auger electron detection is that when using an electron beam theAuger electrons are detected on a baseline of backscattered electrons,and, using an ion beam, the backscattered electrons are not present. Asa result, it can be possible to obtain a relatively high signal to noiseratio for detected Auger electrons while collecting a relatively smallnumber of Auger electrons, which can reduce the amount of time it takesto obtain a relatively good quality Auger electron spectrum from asample when using an ion beam.

C. Scattered Ions

As referred to herein, a scattered ion is generated when an ion from theion beam (e.g., a He ion) interacts with the sample and is scatteredfrom the sample while remaining an ion (e.g., a He ion). Because theprobability that a scattered ion can travel from the sub-surface regionof a sample to the surface of the sample and then be emitted from thesample is very low, scattered ions generally provide information aboutthe surface of the sample. As explained in more detail below, whendetecting scattered ions, the particular arrangement of the detector(s)generally depends on the type of information that is desired to beobtained.

In some embodiments, topographical information about a sample surfacecan be obtained via detected scattered ions. FIG. 34A generally depictsan embodiment of an approach to detecting scattered ions from differentregions of a surface to determine topographical information about thesurface of a sample. In particular, FIG. 34A shows a sample 7010 havingregions 7012, 7014 and 7016 with surfaces 7013, 7015 and 7017,respectively. Scatter patterns 7020, 7030 and 7040 represent the angulardistribution of ions scattered from surfaces 7013, 7015 and 7017,respectively, when the ion beam is perpendicularly incident thereon. Asshown in FIG. 34A, each of scatter patterns 7020, 7030 and 7040 is acosine-type distribution. FIG. 34B depicts the contribution to therelative intensities 7042 and 7052 (dashed line and dotted line,respectively) of scattered ions detected by detectors 7041 and 7050,respectively, arising from topographical effects. Thus, for example,assuming that sample 7010 is formed of the identical material across itsentire surface, the relative total abundance profiles from detectors7041 and 7050 can be used to determine the topography of sample 7010.Alternatively, assuming that the topography of sample 7010 is known,then the contribution to the total abundance of the scattered ionsdetected that is due to topography alone (relative intensities 7042 and7052) can be removed from the total abundance of the detected scatteredions to determine the contribution to the total detected scattered ionsdue to other effects (e.g., changing material across the surface ofsample 7010). Although the detectors can be positioned as desired withrespect to the surface, in certain embodiments, for a detector system ofthe type shown in FIG. 34A, topographic information is obtained from Heions that are scattered at large scattering angles. As an example, insome embodiments, topographic information from scattered ions isdetermined by detecting scattered ions at an angle of 60° or greater(e.g., 65° or greater, 70° or greater, 75° or greater) relative to thedirection of the ion beam. While FIG. 34A depicts the use of twodetectors, in some embodiments a single detector is used (e.g., detector7041 or detector 7050). Alternatively, in certain embodiments, more thantwo (e.g., three, four, five, six, seven, eight) detectors can be used.In general, when multiple detectors are used to detect scattered ions,the detectors are equally spaced from each other with respect to theirsolid angle relative to the surface of the sample. The use of more thantwo detectors (e.g., four detectors) that are symmetrically positionedwith respect to the surface of the sample can allow for detectingsurface features in both orthogonal directions with respect to thenominal plane of the sample surface.

FIGS. 35A-35I generally depict various embodiments of approaches todetecting scattered ions from different regions of a surface todetermine topographical information about the surface of a sample. Inparticular, FIGS. 35A, 35D and 35G shows a sample 8050 having regions8052, 8054, 8056 and 8058 with surfaces 8053, 8055, 8057, 8059 and 8061,respectively. As shown in FIGS. 35A, 35D and 35G, surfaces 8055 and 8059are oblique relative to surfaces 8053, 8057 and 8061. Scatter patterns8070, 8090 and 80110 represent the angular distribution of ionsscattered from surfaces 8053, 8057 and 8061, respectively, when the ionbeam is perpendicularly incident thereon. As shown in FIGS. 35A, 35D and35G, each of scatter patterns 8070, 8090 and 80110 is a cosine-typedistribution. Scatter patterns 8080 and 80100 represent the angulardistribution of ions scattered from surfaces 8055 and 8059 when the ionbeam is perpendicular with respect to regions 8054 and 8058. As shown inFIGS. 35A, 35D and 35G, because the ion beam is not perpendicularlyincident on surfaces 8055 and 8059, the angular distribution of scatterpatterns 8080 and 80100 is not a cosine-type distribution.

FIGS. 35B and 35C depict the total yield of scattered ions and therelative abundance of detected scattered ions when a hemisphericaldetector (which may be capable of angularly resolving the scatteredions, spectrally-resolving the scattered ions, or both) 80120 is used todetect the scattered ions. As shown in FIG. 35C, there is a shadoweffect in the relative abundance of the detected ions when usingdetector 80120. Thus, for example, assuming that sample 8050 is formedof the identical material across its entire surface, the relativeabundance profiles from detector 80120 can be used to determine thetopography of sample 8050. Alternatively, assuming that the topographyof sample 8050 is known, then the contribution to the total abundance ofthe scattered ions detected that is due to topography alone (therelative abundance in FIG. 35D) can be removed from the total abundanceof the detected scattered ions to determine the contribution to thetotal detected scattered ions due to other effects (e.g., changingmaterial across the surface of sample 8050).

FIGS. 35E and 35F depict the total yield of scattered ions and therelative abundance of detected scattered ions when a top detector 80130having a relatively small acceptance angle for scattered ions is used todetect the scattered ions. As shown in FIG. 35F, because the scatteryield into the acceptance angle of detector 80130 is substantiallysmaller at regions 8054 and 8056 (despite the fact that, as shown inFIG. 35E the total yield of scattered ions is higher at these regions),the relative abundance of scattered ions decreases at regions 8054 and8056. Thus, for example, assuming that sample 8050 is formed of theidentical material across its entire surface, the relative abundanceprofiles from detector 80130 can be used to determine the topography ofsample 8050. Alternatively, assuming that the topography of sample 8050is known, then the contribution to the total abundance of the scatteredions detected that is due to topography alone (the relative abundance inFIG. 35D) can be removed from the total abundance of the detectedscattered ions to determine the contribution to the total detectedscattered ions due to other effects (e.g., changing material across thesurface of sample 8050).

FIGS. 35H and 35I depict the total yield of scattered ions and therelative abundance of detected scattered ions when a top detector 80140a relatively large acceptance angle for scattered ions is used to detectthe scattered ions. As shown in FIG. 35I, by selecting the appropriateacceptance angle of detector 80140, the relative abundance of thedetected scattered ions is substantially the same across the sample.Changes in the total abundance of detected scattered ions would be dueto effects other than changes in surface topography (e.g., changingmaterial across the surface of sample 8050).

In certain embodiments, the detection of scattered ions can be used todetermine material constituent information about the surface of thesample. One such approach involves measuring the total abundance ofscattered ions. The total abundance of scattered ions can be detectedusing a single detector (e.g., a hemispherical detector) configured todetect scattered ions leaving surface 181 of sample 180 (the surface onwhich the ion beam impinges), or multiple detectors (e.g., located atdifferent solid angles with respect to the surface of the sample)configured to detect scattered ions leaving surface 181 of sample 180(the surface on which the ion beam impinges the sample surface at arange of angles and energies). In general, the scattering probability ofa He ion (and therefore the total abundance of scattered He ions,assuming no effects from other factors, such as topographical changes inthe surface sample) is approximately proportional to the square of theatomic number (Z value) of the surface atom from which the He ionscatters. Thus, as an example, when trying to distinguish a copper(atomic number 29) line from silicon (atomic number 14) in asemiconductor article, the total abundance of scattered He ions from acopper atom at a surface of the semiconductor article will beapproximately four times the total abundance of scattered ions from asilicon atom at the surface of the semiconductor article. As anotherexample, when trying to distinguish a tungsten (atomic number 74) plugfrom silicon (atomic number 14) in a semiconductor article, the totalabundance of scattered He ions from a tungsten atom at a surface of thesemiconductor article will be approximately 25 times the total abundanceof scattered ions from a silicon atom at the surface of thesemiconductor article. As a further example, when trying to distinguishgold (atomic number 79) region from silicon (atomic number 14) in asemiconductor article, the total abundance of scattered He ions from agold atom at a surface of the semiconductor article will beapproximately 25 times the total abundance of scattered ions from asilicon atom at the surface of the semiconductor article. As anadditional example, when trying to distinguish indium (atomic number 49)from silicon (atomic number 14) in a semiconductor article, the totalabundance of scattered He ions from a indium atom at a surface of thesemiconductor article will be approximately 10 times the total abundanceof scattered ions from a silicon atom at the surface of thesemiconductor article.

Another approach to determining material constituent information aboutthe surface of a sample by detecting scattered He ions (which may beused in combination with or instead of total abundance detection)involves measuring the scattered He ions in an energy-resolved andangle-resolved fashion. For example, as shown in FIG. 36, second lens226 focuses He ion beam 192 onto surface 181 of sample 180. He ions 1102scatter from surface 181 and are detected by detector 1100. Detector1100 is designed so that the angle and energy of each detected scatteredHe ion is known for each angle ε within the acceptance angle of detector1100. By measuring the energy and scattering angle of the scattered Heion, the mass of the atom at the surface that scatters the scattered Heion can be calculated based on the following relationship:$\frac{E_{s}}{E_{i}} = {1 - {\frac{2M_{He}M_{a}}{\left( {M_{He} + M_{a}} \right)^{2}}\left( {1 - {\cos\quad\theta_{s}}} \right)}}$where E_(s) is the energy of the scattered He ion, E_(i) is the incidentenergy of the He ion, M_(He) is the mass of the He ion, θ_(s) is thescattering angle, and M_(a) is the mass of the atom that scatters the Heion.

Detector 1100 can, for example, be an energy-resolving phosphor-baseddetector, an energy-resolving scintillator-based detector, a solid statedetector, an energy-resolving electrostatic prism-based detector, anelectrostatic prism, an energy-resolving ET detector, or anenergy-resolving microchannel. In general, it is desirable for detector1100 to have a substantial acceptable angle. In some embodiments,detector 1100 is stationary (e.g., an annular detector). In certainembodiments, detector 1100 can sweep through a range of solid angles.Although a system for detecting energy-resolved and angle-resolvedscattered He ions that includes a single detector has been described,such a system can contain multiple (e.g., two, three, four, five, six,seven, eight) detectors. Often, the use of multiple detectors isdesirable because it can allow for a larger acceptance angle of detectedscattered He ions.

In some embodiments, detecting the total abundance of scattered He ionscan provide crystalline information about a sample. The total abundanceof scattered He ions can vary depending on whether the ion beam isaligned with the crystal structure of the sample or not. If the ion beamis aligned with the crystal structure of the sample, the probabilitythat ions in the ion beam can generally penetrate into a given distanceinto the sample without undergoing a collision with a sample atom(commonly referred to as channeling) is relatively high, resulting in alower total abundance of scattered He ions. If, on the other hand, theion beam is not aligned with the crystal structure, then the ions in theion beam will have a lower probability of penetrating into the samplethe given distance without undergoing a collision with a sample atom,resulting in a higher total abundance of scattered He ions. Therefore,the change in the total abundance of scattered He ions as a function ofthe ion beam location at the sample surface can be correlated to thecrystalline information of the material at that location. For example,there may be regions of the sample surface where the scattered He ions'total abundance is substantially the same. Such regions can, forexample, have the same crystal orientation, and the size of the regionscan provide grain size and/or crystal size information (e.g., in apolycrystalline sample that includes multiple, oriented crystaldomains), and/or can provide information regarding strained regions ofsample (whether amorphous or crystalline) because the magnitude of thescattered He ions' total abundance for a material of a given chemicalcomposition (e.g., elemental composition, material composition) candepend on the strain of the material.

Alternatively or additionally, crystalline information about the surfaceof a sample can be obtained by exposing a region of the surface to anion beam (without rastering the ion beam) and then measuring a patternof the scattered He ions (e.g., similar to a Kikuchi pattern obtaineddue to backscattered electrons from a sample surface exposed to anelectron beam). The pattern of the scattered He ions can be analyzed todetermine, for example, the orientation, lattice spacing, and/or crystaltype (e.g., body centered cubic, face centered cubic) of the material atthe location of the sample surface that is exposed to the ion beam.

Scattered ion imaging techniques can be applied to a variety ofdifferent classes of samples. An example of such a class of materials issemiconductor articles, such as patterned wafers, which can include, forexample, multiple electrical conductors surrounded by a matrix ofinsulating material. Scattered ion imaging techniques can be used toidentify defects in the device, such as incomplete electricalconnections between conductors, and/or electrical shorts between circuitelements. Optionally, this approach can similarly be used for purposesof mask repair. Another example of a sample class for which scatteredion imaging techniques can be used is metals and alloys. For example,images of samples that contain mixed materials such as alloys can beused to determine the surface distribution of each of the materials inthe sample. Yet another example of a sample class where scattered ionimaging techniques can be used is read/write structures for datastorage. Additional examples of classes of materials for which scatteredion imaging techniques can be used are biological materials andpharmaceutical materials.

In general, scattered ions are not formed when a sample surface isexposed to an electron beam of the type used in conventional SEMs, andthus none of the crystalline information or material constituentinformation obtainable via detected scattered He ions is available withsuch SEMs. This is a significant advantage of a gas field ion microscope(e.g., a He ion microscope) as described herein relative to aconventional SEM.

Measurement of scattered He ions using a gas field ion microscope (e.g.,a He ion microscope) as described herein can offer a number ofadvantages relative to conventional Rutherford backscatteringmeasurement devices. The spot size to which the incident He ions can befocused at the surface of the sample can be significantly smaller thanthe spot size of conventional Rutherford backscattering measurementdevices (typical spot sizes of 100 μm to 1 mm or more), allowing for thematerial constituent information about the sample surface to be moreprecisely localized than achieved with conventional Rutherfordbackscattering measurement devices. Further, a gas field ion microscope(e.g., a He ion microscope) as described herein allows forpixel-by-pixel rastering across the sample surface, whereas Rutherfordbackscattering measurement devices do not have this capability. This canreduce the cost and/or complexity associated with material constituentinformation about the sample surface at various locations of thesurface.

D. Primary Neutral Particles

As referred to herein, a primary neutral particle is a neutral particlegenerated when the ion beam interacts with the sample and an ion (e.g.,a He ion) from the ion beam leaves the sample as an un-charged neutralparticle (e.g., an un-charged He atom). In contrast to scattered Heions, primary He atoms are a relatively sensitive probe of thesub-surface region of a sample. As used herein, the sub-surface regionis the region of a sample that is more than five nm beneath the samplesurface (e.g., 10 nm or more beneath the sample surface, 25 nm or morebeneath the sample surface, 50 nm or more beneath the sample surface),and 1000 nm or less beneath the sample surface (e.g., 500 nm or lessbeneath the sample surface, 250 nm or less beneath the sample surface,100 nm or less beneath the sample surface). In general, the probe depthof the ion beam increases as the energy of the ions increase. Thus, todetermine deeper sub-surface information about a sample, a higher energyion beam can be used. A depth profile of material constituentinformation can be obtained by taking multiple He atom images of asample at varying ion beam energies (probe depths). In some embodiments,tomographic reconstruction algorithms and/or techniques can be appliedto the depth dependent information to perform tomographic reconstructionof the structure of the sample.

In general, material constituent information based on the detection ofprimary He atoms can be determined using total abundance detection,energy-resolved/angle-resolved detection, or both, using detectorarrangements as described above with respect to the correspondingtechniques for scattered He ions and also using the same mathematicalrelationships as described above for scattered He ions. Typically,however, the detector(s) used for primary He atoms is capable ofdetecting a neutral species. Examples of such detectors includemicrochannel plates, channeltrons and scintillator/PMT detectors.

Primary neutral particle (e.g., He atom) techniques can be applied to avariety of different classes of samples. An example of such a class ofmaterials is semiconductor articles, such as patterned wafers, which caninclude, for example, multiple electrical conductors surrounded by amatrix of insulating material. Primary neutral particle techniques canbe used to identify defects in the device, such as incomplete electricalconnections between conductors, and/or electrical shorts between circuitelements. Optionally, this approach can similarly be used for purposesof mask repair. Another example of a sample class for which primaryneutral particle imaging techniques can be used is metals and alloys.For example, images of samples that contain mixed materials such asalloys can be used to determine the surface distribution of each of thematerials in the sample. Yet another example of a sample class whereprimary neutral particle imaging techniques can be used is read/writestructures for data storage. Additional examples of classes of materialsfor which primary neutral particle imaging techniques can be used arebiological materials and pharmaceutical materials.

Primary neutral particles are generally not generated when a samplesurface is exposed to an electron beam of the type used in conventionalSEMs, and thus none of the crystalline information or materialconstituent information obtainable via detected scattered He ions isavailable with such SEMs. This is a significant advantage of a gas fieldion microscope (e.g., a He ion microscope) as described herein relativeto a conventional SEM.

E. Photons

Typical photons of interest include X-ray photons, UV photons, visiblephotons and IR photons. As referred to herein, an IR photon is a photonhaving a wavelength of more than 700 nm to 100,000 nm (e.g., from1.2×10⁻⁵ keV to 1.7×10⁻³ keV), a visible photon is a photon having awavelength of from more than 400 nm to 700 nm (e.g., from 1.8×10⁻³ keVto 3×10⁻³ keV), a UV photon is a photon having a wavelength of more than10 nm to 400 nm (e.g., from 3×10⁻³ keV to 125 eV) and an X-ray photon isa photon having a wavelength of from 0.01 nm to 10 nm (e.g., from 125 eVto 125 keV). In general, such photons are emitted from the samplesurface at a range of angles and energies/wavelengths. However, theinformation of most interest is usually the wavelength and/or energy ofthe photons (as opposed to angle-resolved photon information) because,as explained below, the wavelength and/or energy of the photons is whatcan provide information regarding the sample surface. The photons can bedetected using one or more appropriate detectors capable of detectingphotons in a wavelength-resolved or energy-resolved fashion (seediscussion above regarding types of detectors). If multiple detectorsare used, the detectors may all be the same type of detector, ordifferent types of detectors may be used, and may generally beconfigured as desired. The detectors can be configured to detect photonsleaving surface 181 of sample 180 (the surface on which the ion beamimpinges), surface 183 of sample 180 (the surface on the opposite sidefrom where the ion beam impinges) or both (see discussion aboveregarding configurations of detectors). To enhance the signal to noiseof the detected photons, it can be desirable to use a detector that cancollect a relatively large solid angle of photons. Additionally oralternatively, the system can include one or more optical elements(e.g., one or more lenses, one or more mirrors) that are adjacent thesurface of the sample and that can direct the photons to the detectorcan be used (e.g., to increase the effective solid angle of detection ofthe detected photons).

In general, detecting the energy and/or wavelength of the photons canyield material constituent information (e.g., elemental information,chemical environment information) about a sample. In such embodiments,the information is predominantly related to the surface of the sample.In general, for each element or material in a given chemicalenvironment, the photons emitted by the element or material will have aparticular energy/band of energies and wavelength/band of wavelengths.As a result, the energy and wavelength of the photons emitted from agiven location on a surface generally depends on the material present atthat location. Therefore, the change in the energy or wavelength of thephotons as a function of the location of the ion beam on the surface ofthe sample, can be correlated to a change in the element(s) and/ormaterial(s) present at the surface of the sample, providing materialconstituent information about the surface of the sample.

Alternatively or additionally, material constituent information aboutthe sample can be obtained detecting photons by determining thede-excitation time of the sample material. This can be achieved, forexample, by pulsing the ion beam to expose the sample to the ion beamfor a brief period, followed by measuring the amount of time it takes todetect the photons, which relates to the de-excitation time of thesample material that emits the photons. In general, each element ormaterial in a given chemical environment will have a particularde-excitation time period.

Crystalline information about a sample can be obtained using photondetection in combination with a polarizer because the polarization ofthe photons can depend upon the crystal orientation of the material inthe sample. Thus, via the use of a polarizer, the polarization of thephotons emitted by a sample can be determined, providing informationrelating to the crystal orientation of the sample.

In general, the information contained in the detected photons willpredominantly be information about the surface of the sample. However,because photons can escape from a sub-surface region of a sample,detected photons can contain information relating to the sub-surfaceregion of the sample. Thus, detected photons can be used to determineoptical properties of the sample. For example, the transparency of thesample to the photons can be investigated by manipulating the energy ofthe ions in the ion beam, and therefore their probe depth, anddetermining the corresponding impact on the intensity of the detectedphotons. The detected photon intensity as a function of ion energy(probe depth) can yield information regarding the transparency of thesample to the photons.

Photon imaging techniques can be applied to a variety of differentclasses of samples. An example of such a class of materials issemiconductor articles, such as patterned wafers, which can include, forexample, multiple electrical conductors surrounded by a matrix ofinsulating material. Photon imaging techniques can be used to identifydefects in the device, such as incomplete electrical connections betweenconductors, and/or electrical shorts between circuit elements.Optionally, this approach can similarly be used for purposes of maskrepair. Another example of a sample class for which photon imagingtechniques can be used is metals and alloys. For example, images ofsamples that contain mixed materials such as alloys can be used todetermine the surface distribution of each of the materials in thesample. Yet another example of a sample class where photon imagingtechniques can be used is read/write structures for data storage.Additional examples of classes of materials for which photon imagingtechniques can be used are biological materials and pharmaceuticalmaterials.

Imaging samples using photons generated by exposure to a He ion beam canprovide a number of advantages relative to photon imaging via othertechniques, such as SEM. For example, the spot size of the He ion beamon the sample can be smaller than the spot size of an electron beam froma SEM. As a result of the smaller spot size, the region of the samplethat is exposed to the He ion beam is more carefully controlled than theexposed region in a SEM.

Further, in general, because He ions are heavier than electrons,scattering events do not disperse He ions as readily within the sampleas electrons are dispersed by scattering. As a result, He ions incidenton the surface of a sample can interact with the sample in a smallerinteraction volume than electrons in a SEM. As a result, photonsdetected in a gas field ion microscope (e.g., a He ion microscope) canarise from a smaller region than the region giving rise to photons in aSEM with a similar spot size. Consequently, the photons which aregenerated by the interaction of the sample and the He ion beam cancorrespond to a more localized interrogation of the surface of thesample (e.g., with less lateral averaging of material properties) thanthe photons generated in a SEM.

In addition, the He ion source also provides a greater depth of focusthan an electron source. As a result, images of a sample obtained usingan ion microscope (e.g., a gas field ion microscope) can show a largerportion of the sample, measured along the direction perpendicular to thesample surface, in focus than comparable images obtained from photons ina SEM.

F. Secondary Ions

As referred to herein, a secondary ion is an ion formed when the ionbeam interacts with the sample to remove a mono-atomic or poly-atomicspecies from the sample in a charged state. Interactions between theincident ion beam and the sample can produce secondary ions. Typically,this method is more effective when using a noble gas ion of mass greaterthan He (Ar ions, Ne ions, Kr ions, Xe ions).

Detection of secondary ions from the sample can provide materialconstituent information about the sample via calculation of the massesof detected particles. In general, this information will correspond tomaterial at the surface of the sample. In some embodiments, the mass(es)of the secondary ions is(are) determined using a combination oftime-of-flight and a mass-resolved detector, such as a quadrupole massspectrometer. Such secondary ion detection can be performed as follows.The ion beam is operated in pulsed mode by changing the electricalpotentials applied to ion optical elements in the ion optics. Pulses ofincident ions are incident on a surface of the sample. A clock signal,which determines the rate at which the ion optical element potentialsare switched to turn the ion beam on and off, is also used as areference time signal for the detector (see discussion above regardingdetectors). In this manner, the time of flight of secondary ions fromthe sample to the detector can be accurately determined.

Based upon a detected secondary ions' time of flight, its distancetraveled (e.g., the distance between the detector and the sample), andits energy, the mass of the particle can be calculated, and the type ofchemical species (e.g., atom) can be identified. This information isused to determine material constituent information for the sample.

Secondary ion imaging techniques can be applied to a variety ofdifferent classes of samples. An example of such a class of materials issemiconductor articles, such as patterned wafers, which can include, forexample, multiple electrical conductors surrounded by a matrix ofinsulating material. Secondary ion imaging techniques can be used toidentify defects in the device, such as incomplete electricalconnections between conductors, and/or electrical shorts between circuitelements. Optionally, this approach can similarly be used for purposesof mask repair. Another example of a sample class for which secondaryion imaging techniques can be used is metals and alloys. For example,images of samples that contain mixed materials such as alloys can beused to determine the surface distribution of each of the materials inthe sample. Yet another example of a sample class where secondary ionimaging techniques can be used is read/write structures for datastorage. Additional examples of classes of materials for which secondaryion imaging techniques can be used are biological materials andpharmaceutical materials.

Secondary ions are generally not generated when a sample surface isexposed to an electron beam of the type used in conventional SEMs, andthus none of the material constituent information obtainable viadetected secondary ions is available with such SEMs. This is asignificant advantage of a gas field ion microscope (e.g., a He ionmicroscope) as described herein relative to a conventional SEM.

G. Secondary Neutral Particles

A secondary neutral particle is a neutral particle generated when theion beam interacts with the sample to remove a mono-atomic orpoly-atomic species from the sample in an un-charged state. Interactionsbetween the incident ion beam and the sample can produce secondaryneutral particles. Typically, this method is more effective when using anoble gas ion of mass greater than He (Ar ions, Ne ions, Kr ions, Xeions). In general, to access the information available from secondaryneutral particles, the particles are ionized (e.g., via laser inducedionization, electron induced ionization) prior to detection.

Detection of secondary neutral particles (post-ionization) from thesample can provide material constituent information about the sample viacalculation of the masses of detected particles. In general, thisinformation will correspond to material at the surface of the sample. Insome embodiments, the mass(es) of the secondary neutral particles(post-ionization) is(are) determined using a combination oftime-of-flight and a mass-resolved detector, such as a quadrupole massspectrometer. Such secondary neutral particle (post-ionization)detection can be performed as follows. The ion beam is operated inpulsed mode by changing the electrical potentials applied to ion opticalelements in the ion optics. Pulses of incident ions are incident on asurface of the sample. A clock signal which determines the rate at whichthe ionization device (e.g., laser, electron beam) and/or ion opticalelement potentials are switched is also used as a reference time signalfor the detector (see discussion above regarding detectors). In thismanner, the time of flight of secondary neutral particles (postionization) from the sample to the detector can be accuratelydetermined.

Based upon a detected secondary ions' time of flight, its distancetraveled (e.g., the distance between the detector and the sample), andits energy, the mass of the particle can be calculated, and the typechemical species (e.g., atom) can be identified. This information isused to determine material constituent information for the sample.

Secondary neutral particle imaging techniques can be applied to avariety of different classes of samples. An example of such a class ofmaterials is semiconductor articles, such as patterned wafers, which caninclude, for example, multiple electrical conductors surrounded by amatrix of insulating material. Secondary neutral particle imagingtechniques can be used to identify defects in the device, such asincomplete electrical connections between conductors, and/or electricalshorts between circuit elements. Optionally, this approach can similarlybe used for purposes of mask repair. Another example of a sample classfor which secondary neutral particle imaging techniques can be used ismetals and alloys. For example, images of samples that contain mixedmaterials such as alloys can be used to determine the surfacedistribution of each of the materials in the sample. Yet another exampleof a sample class where secondary neutral particle imaging techniquescan be used is read/write structures for data storage. Additionalexamples of classes of materials for which secondary neutral particleimaging techniques can be used are biological materials andpharmaceutical materials.

Secondary neutral particle are generally not generated when a samplesurface is exposed to an electron beam of the type used in conventionalSEMs, and thus none of the material constituent information obtainablevia detected secondary neutral particle is available with such SEMs.This is a significant advantage of a gas field ion microscope (e.g., aHe ion microscope) as described herein relative to a conventional SEM.

Exemplary Applications

A. Semiconductor Fabrication

(i) General

Semiconductor fabrication typically involves the preparation of anarticle that includes multiple layers of materials sequentiallydeposited and processed to form an integrated electronic circuit, anintegrated circuit element, and/or a different microelectronic device.Such articles typically contain various features (e.g., circuit linesformed of electrically conductive material, wells filled withelectrically non-conductive material, regions formed of electricallysemiconductive material) that are precisely positioned with respect toeach other (e.g., generally on the scale of within a few nanometers).The location, size (length, width, depth), composition (chemicalcomposition) and related properties (conductivity, crystallineorientation, magnetic properties) of a given feature can have animportant impact on the performance of the article. For example, incertain instances, if one or more of these parameters is outside anappropriate range, the article may be rejected because it cannotfunction as desired. As a result, it is generally desirable to have verygood control over each step during semiconductor fabrication, and itwould be advantageous to have a tool that could monitor the fabricationof a semiconductor article at various steps in the fabrication processto investigate the location, size, composition and related properties ofone or more features at various stages of the semiconductor fabricationprocess. As used herein, the term semiconductor article refers to anintegrated electronic circuit, an integrated circuit element, amicroelectronic device or an article formed during the process offabricating an integrated electronic circuit, an integrated circuitelement, a microelectronic device. In some embodiments, a semiconductorarticle can be a portion of a flat panel display or a photovoltaic cell.

Regions of a semiconductor article can be formed of different types ofmaterial (electrically conductive, electrically non-conductive,electrically semiconductive). Exemplary electrically conductivematerials include metals, such as aluminum, chromium, nickel, tantalum,titanium, tungsten, and alloys including one or more of these metals(e.g., aluminum-copper alloys). Exemplary electrically non-conductivematerials include borides, carbides, nitrides, oxides, phosphides,silicides, and sulfides of one or more of the metals (e.g., nickelsilicides, tantalum borides, tantalum germaniums, tantalum nitrides,tantalum silicides, tantalum silicon nitrides, and titanium nitrides).Exemplary electrically semiconductive materials include silicon,germanium and gallium arsenide. Optionally, a electricallysemiconductive material can be doped (p-doped, n-doped) to enhance theelectrical conductivity of the material.

As noted above, in general, fabrication of a semiconductor articleinvolves sequentially depositing and processing multiple layers ofmaterial. Typical steps in the deposition/processing of a given layer ofmaterial include imaging the article (e.g., to determine where a desiredfeature to be formed should be located), depositing an appropriatematerial (e.g., an electrically conductive material, an electricallysemiconductive material, an electrically non-conductive material) andetching to remove unwanted material from certain locations in thearticle. Often, a photoresist, such as a polymer photoresist, isdeposited/exposed to appropriate radiation/selectively etched to assistin controlling the location and size of a given feature. Typically, thephotoresist is removed in one or more subsequent process steps, and, ingeneral, the final semiconductor article desirably does not contain anappreciable amount of photoresist.

The gas field ion microscope (e.g., He ion microscope) described hereincan be used to investigate a semiconductor article at various steps(e.g., each step) in the fabrication process. In particular, bydetecting and analyzing one type of particle or multiple different typesof particles (see discussion above), the gas field ion microscope (e.g.,He ion microscope) can be used to determine topographical informationabout the surface of the semiconductor article, material constituentinformation of the surface of the semiconductor article, materialconstituent information about the sub-surface region of thesemiconductor article, crystalline information about the semiconductorarticle, voltage contrast information about the surface of thesemiconductor article, voltage contrast information about a sub-surfaceregion of the sample, magnetic information about the semiconductorarticle, and/or optical information about the semiconductor article.

Using an ion microscope or ion beam as described herein can provide avariety of different advantages, which, in general, can reduce the time,cost and/or complexity associated with semiconductor articlefabrication. Exemplary advantages associated with using the ionmicroscope or ion beam described herein include relatively highresolution, relatively small spot size, relatively little undesirablesample damage, relatively little undesirable material deposition and/orimplantation, relatively high quality imaging in a relatively short timeperiod, relatively high throughput.

Certain examples of process steps in semiconductor fabrication arediscussed below.

(ii) Maskless Lithography

Semiconductor articles are typically prepared using a lithographyprocess that involves putting a layer of photoresist (e.g., polymerphotoresist, such as poly(methyl methacrylate) (PMMA) or epoxy-basedphotoresists, allyl diglycol carbonate, or photosensitive glasses) on asurface, patterning the material so that certain regions of thephotoresist are resistant to an etchant (and some regions are notresistant to an etchant), etching the non-etch resist regions of thematerial, depositing appropriate materials (e.g., one or moreelectrically conductive materials, one or more non-electricallyconductive materials, one or more semiconductive materials), andoptionally removing undesired regions of material. Typically, thepatterning step involves exposing the photoresist to a radiation patternof an appropriate wavelength so that some regions of the photoresist areetch resistant and other regions of the photoresist are not etchresistant.

The radiation pattern can be formed on the photoresist by forming animage of a mask onto the photoresist or covering certain regions of thephotoresist with a mask, and exposing the uncovered regions of thephotoresist through the mask. However, rather than using a mask to coverregions of photoresist prior to exposure to radiation, an ion beamgenerated by the interaction of gas atoms with the gas field ion source(e.g., He ion source) described herein can be used to irradiate topattern the photoresist to create desired etch-resistant regions andnon-etch resistant regions. This can be achieved, for example, byrastering the ion beam across the photoresist so that desired regions ofmaterial are exposed to the ions (e.g., by turning the ion beam on atregions where exposure of the photoresist to radiation is desired and byturning the ion beam off at regions where exposure of the photoresist toradiation is not desired). As a result, a semiconductor article can befabricated in a maskless process.

Using the ion beam generated via the interaction of gas atoms with thegas field ion source (e.g., He ion source) disclosed herein can offerone or more of the following advantages. As noted, the process can beperformed without the use of mask, which can decrease the time, costand/or complexity associated with fabrication of semiconductor articles.The relatively large depth of focus of the ion beam can allow forpatterning relatively thick photoresist materials (e.g., 2 μm or morethick, 5 μm or more thick, 10 μm or more thick, and or 20 μm or lessthick). The relatively deep penetration depth of ions that can beachieved with the ion beam can further assist in processing relativelythick photoresist materials, as well as assisting in good qualityprocessing of more standard thickness photoresist materials. Inaddition, the ion beam has higher resolution relative to what isgenerally achieved with an electron beam, allowing for the fabricationof smaller sized features with higher precision. Further, ion beampatterning of photoresist can be faster than electron beam patterning ofphotoresist.

(iii) Combination of Ion Microscope and Focused Ion Beam

A focused ion beam (FIB) is commonly used during the fabrication of asemiconductor article to obtain a sample for inspection. Gallium (Ga)ions are commonly used in the FIB. A FIB can be used for a variety ofreasons, such as cross-sectional imaging through a semiconductorarticle, circuit editing, failure analysis of a semiconductor articles,preparation of a semiconductor article specimen for transmissionelectron microscopy (TEM) and mask repair. Optionally, a FIB can be usedto deposit one or more materials on a sample (e.g., as an ion source ina chemical vapor deposition process). Typically, the FIB is used toremove material from a semiconductor article via sputtering. Forexample, in some embodiments, the FIB is used to slice through asemiconductor article to expose a cross-section of the article forsubsequent imaging using the ion microscope. In certain embodiments, theFIB is used to sputter away material from an article to form a trench orvia in the article. This technique can be used, for example, to exposeportions of the article that are underneath the article's surface. Theion microscope can then be used to deposit new material, or etch awayexisting material exposed by the FIB, using gas assisted chemicaltechniques. In some embodiments, a FIB can also be used as a selectivesputtering tool to remove portions of a semiconductor article, such asportions of conductive material on the article. In certain embodiments aFIB is used to cut out a portion of a sample so that the portion can besubsequently analyzed (e.g., using TEM).

It is generally desirable to precisely locate the FIB on the sample. Agas field ion microscope (e.g., a He ion microscope) as described hereincan be used for this purpose. For example, a cross-beam tool with both aFIB instrument and a gas field ion microscope can be used so that thelocation of the FIB can be determined using the gas field ion microscopewithout moving the sample. With such a tool, the gas field ion sourcecan be used to image the sample and provide information that can be usedto precisely position the FIB as desired. Such an arrangement can offernumerous advantages relative to using a SEM to determine location of theFIB. As an example, use of a SEM can result in a magnetic field adjacentthe sample surface, which can result in isotope separation of the Gaions, resulting more than one location of the FIB at the sample. In manyinstances, this problem results in the FIB and SEM being used in seriesrather than simultaneously. In contrast, however, a gas field ionmicroscope can be operated in the absence of such a magnetic field,thereby eliminating complications associated with Ga ion isotopeseparation, while also allowing the FIB and gas field ion microscope tobe used simultaneously. This can be desirable, for example, whenpreparing a sample for subsequent inspection (e.g., for TEM inspection)where it may be desirable for the thickness of the sample to satisfyrelatively strict tolerances. An additional advantage for using a gasfield ion microscope (e.g., a He ion microscope) is that it has a longerworking distance than typically used with a SEM, while still maintainingvery good resolution because the ion beam has a smaller virtual sourcethan the electron beam. This can relieve certain spacing constraintsthat may exist for a tool that combines a FIB instrument and a SEM. Afurther advantage of a gas field ion microscope as described herein isthat it can be used to obtain sub-surface information about a sample,which can enhance the ability to precisely locate the FIB, whereas a SEMgenerally cannot provide such sub-surface information.

(iv) Gas Assisted Chemistry

Gas assisted chemistry is commonly used during semiconductor fabricationto add material to and/or remove material from a given layer. Forexample, gas assisted chemistry can be used for semiconductor circuitediting—to repair damaged or incorrectly fabricated circuits formed insemiconductor articles. Gas assisted chemistry can also be used inphotolithographic mask repair, where material can be added to or removedfrom masks to repair defects which result from use or incorrectfabrication.

The process generally involves interacting electrons with an activatinggas to form a reactive gas that can then participate in chemistry at thesurface of a semiconductor article to add material to the surface,remove material from the surface, or both. Typically, the electrons aregenerated as secondary electrons resulting from the interaction of a Gaion beam with the sample and/or the electrons are generated as secondaryelectrons resulting from the interaction of an electron beam (e.g.,produced by a SEM) with the sample. Optionally, an appropriate pumpingsystem can be used to remove undesirable volatile products of thesurface chemistry.

Examples of activating gases that can be used to remove material fromthe surface include Cl₂, O₂, I₂, XeF₂, F₂, CF₄ and H₂O. As an example,in some embodiments, a surface region formed of chrome, chrome oxide,chrome nitride and/or chrome oxynitride can be at least partiallyremoved by interacting electrons with Cl₂ and/or O₂, and allowing theresulting chemical species to etch the surface region. As anotherexample, in certain embodiments, a surface region formed of a tantalumnitride can be at least partially removed by interacting electrons withXeF₂, F₂ and/or CF₄, and allowing the resulting chemical species to etchthe surface region. As a further example, in certain embodiments, asurface region formed of a carbon-containing material can be at leastpartially removed by interacting electrons with H₂O and/or O₂, andallowing the resulting chemical species to etch the surface region.

An example of an activating gas that can be used to deposit a materialon the surface is WF₆ (to deposit W, such as a W plug).

An ion beam generated by the interaction of gas atoms with the gas fieldion source (e.g., the He ion source) described herein can be used toperform gas assisted chemistry. In such a process, for example, thesecondary electrons that leave the sample due to the interaction of theion beam with the sample can be the electrons used to assist in thechemistry. Using such an ion beam can offer several advantages relativeto using a Ga ion beam. As an example, undesirable ion implantation canbe reduced (e.g., eliminated) using a He ion beam, whereas undesirableimplantation of Ga is a common problem when a Ga ion beam is used. Asanother example, a gas field ion beam (e.g., a He ion beam) can provideimproved resolution relative to a Ga ion beam and/or an incidentelectron beam (e.g., an incident electron beam produced by a SEM), whichcan allow for the more precise and/or controllable use of the chemistry.This can, for example, reduce (e.g., eliminate) the undesirableinteraction of ions with certain portions of a sample (e.g., such as canoccur with a Ga ion beam where the beam profile has tails that extend toundesirable regions of the sample where Ga implantation can createproblems with the performance of the semiconductor article).

(v) Sputtering

In the process of fabricating semiconductor articles, it can bedesirable during certain steps to remove materials. An ion beam can beused for this purpose where the ion beam sputters material from thesample. In particular, an ion beam generated via the interaction of gasatoms with a gas field ion source as described herein can be used forsputtering a sample. Although He gas ions may be used, it is typicallypreferable to use heavier ions (e.g., Ne gas ions, Ar gas ions, Kr gasions, Xe gas ions) to remove material. During the removal of material,the ion beam is focused on the region of the sample where the materialto be removed is located.

An advantage to using an ion beam to remove material is that thematerial can be removed in a relatively controlled and/or precisemanner. An additional advantage is that sputtering can be achievedwithout undesirable implantation of ions (e.g., such as often resultswhen using Ga ion sputtering, where Ga implantation is a commonundesired side effect of sputtering).

(vi) Detection of Voids

During the fabrication of a semiconductor article, voids in certainfeatures or layers may be inadvertently formed. In some embodiments, thevoids can undesirably impact the properties (e.g., electrical,mechanical) of the feature and/or the overall device. In certainembodiments, subsequent processing steps may open the void, and the voidmay, for example, fill with liquid and/or gaseous components. This cancause corrosion of the underlying structures, particle defects and/orresidue defects on the surrounding wafer surface.

As an example, during W plug deposition from WF₆, a TiN_(x) protectivelayer is commonly used to protect an adjacent dielectric material (e.g.,boron and phosphor doped silicon glass) from corrosion (e.g., from HFthat is liberated during W formation). Discontinuities in the TiN_(x)layer can result in significant void formation. As another example,material (e.g., dielectric material) deposition in trenches (e.g.,relatively high aspect ratio trenches) can result in the formation of abottleneck with subsequent void formation. As an additional example,void formation can occur during dielectric filling of shallow trenchisolation structures. As a further example, voids can be formed duringthe formation of electrically conductive lines of material (e.g., copperlines), which can result in undesirable reduction in electricalconductance. In some cases, such voids can result in a lack ofelectrical conductance where electrical conductance is desired.

A gas field ion microscope (e.g., a He ion microscope) as describedherein can be used to investigate void formation by taking advantage ofits ability to provide sub-surface information about a sample, such as asemiconductor article. This property can be used during thesemiconductor article fabrication process to determine the existenceand/or location of voids. This is a distinct advantage over using anelectron beam because an electron beam generally does not provide thiskind of sub-surface information for a sample.

(vii) Overlay Shift Registration

Overlay shift registration generally refers to the alignment of afeature of a given layer of a semiconductor article with a feature in adifferent layer of the semiconductor article. As noted above, theformation of a semiconductor article generally involves the properformation of many layers. Typically, a semiconductor article containswell over 20 layers. Often, each layer can contain multiple differentfeatures, each of which is desirably located with high precision so thatthe semiconductor article can function properly. As an example, asemiconductor article can contain lateral features, such as electricallyconductive wires, which are in different layers and connected to eachother by a via. In general, it is desirable to have features within thesemiconductor article aligned with each other to within 100 nm (e.g., 75nm, 50 nm, 25 nm, 15 nm, 10 nm, nine nm, eight nm, seven nm, six nm,five nm, four nm, three nm, two nm, 1 nm). Misalignment of a single oneof these many features can render the entire semiconductor articleuseless.

Overlay shift registration is commonly performed using opticaltechniques using test structures, which are μm-sized structures(significantly larger than microelectronic circuit feature sizes). Assuch, optical test structures typically cannot be placed intra-dye on awafer due to the amount of wafer space they occupy. The test structurescan be placed, for example, nearer to the edges of wafer, but they stilloccupy valuable space on the wafer surface. Optical test structures arealso expensive, because they are manufactured only for alignmentpurposes. Finally, the use of optical test structures for alignment haslimitations regarding the precision with which the alignment of featuresin different layers can be determined.

The ability of a gas field ion microscope (e.g., a He ion microscope) asdescribed herein to provide a variety of types of information (e.g.,topographical information, material constituent information about thesurface, material constituent information about a sub-surface region,crystalline information, voltage contrast information about the surface,voltage contrast information about a sub-surface region, magneticinformation, and optical information) about the sample with relativelyhigh precision allows for the microscope to be advantageously usedduring the fabrication of a semiconductor article to assist in assuringthat the features in the device are positioned and dimensioned properlyand with high precision within the device. In particular, the He ionmicroscope can permit alignment of circuit features in multiple layersat higher resolution than can typically be achieved using optical teststructures. Further, overlay shift registration can be performed withoutusing purpose-fabricated test structures (e.g., optical test structures)because, for example, the gas field ion microscope (e.g., He ionmicroscope) described herein can image sub-surface features of samples,such as semiconductor articles. Accordingly, the wasted space on a wafertaken up by purpose-fabricated test structures (e.g., optical teststructures) can be avoided, as well as the associated cost and/orcomplexity associated with including such test structures.

(vii) Critical Dimension Metrology

Critical dimension metrology refers to the measurement of the lineardimensions of features in a semiconductor article that can have acritical impact on the performance of the device. Examples of suchfeatures can include lines (e.g., lines of electrically conductivematerial, lines of electrically semiconductive conductive material,lines of electrically non-conductive material). A semiconductor articlecan contain one or more features having a size dimension of 20 nm orless (e.g., 10 nm or less, five nm or less, four nm or less, three nm orless, two nm or less, one nm or less). In some embodiments, the size ofthe feature is measured multiple times to provide statisticalinformation regarding the size of the feature. Critical dimensionmeasurements frequently involve, e.g., the determination of the lengthof a patterned feature on a wafer, for example. Wafers (containingmultiple dies, with each die forming a semiconductor article) may beselected at random from a fabrication line for inspection, or all waferson the line can be inspected. An imaging instrument can be used tomeasure selected critical dimensions at a relatively high throughputrate. If the measured critical dimension does not fall within acceptablelimits, the wafer may be discarded. If multiple samples originating froma particular fabrication machine have critical dimensions outsideacceptable limits, the machine may be taken out of service, or itsoperating parameters changed.

The He ion microscope systems disclosed herein can be used for criticaldimension measurement. In particular, the He ion beam can beraster-scanned over a region of a wafer, and the resulting image(s) ofthe wafer can be used to determine the critical dimension(s). Withregard to critical dimension measurement, He ion microscope systems canprovide a number of advantages relative to SEMs and other inspectionsystems. He ion microscope images generally exhibit less edge blooming(generally, excessive signal, approaching the point of saturation of thedetector, due to enhanced yield at topographic features with slopesnearly parallel to the beam) than comparable SEM images. The reducededge blooming is a result of the smaller interaction volume between Heions and the surface of the sample, relative to the interaction volumeof electrons with the surface.

In addition, the incident He ions can be focused to a smaller spot sizethan a comparable incident electron beam. The smaller beam spot size, incombination with the smaller interaction volume, results in images ofthe sample having resolution that is superior to images produced withSEMs, and more accurate determination of critical dimensions of samples.

The depth of focus of a He ion beam is relatively large compared to aSEM. As a result, the resolution of sample features at varying depths ismore consistent when using an ion beam, as compared to an electron beam.Therefore, using an ion beam can provide information at various sampledepths with better and more consistent lateral resolution than can beprovided using an electron beam. As an example, better criticaldimension profiles can be achieved using an ion beam than can beachieved with an electron beam.

Further, in embodiments in which information is obtained based at leastin part on secondary electrons, the relatively high yield of secondaryelectrons provided by an ion beam, as compared to an electron beam, canresult in a relatively high signal to noise ratio for a given current.This can, in turn, allow for sufficient information about the sample tobe obtained in a relatively short period of time, increasing throughputfor a given current.

Imaging of the samples for determination of critical dimensions can beperformed using scattered He ions. This provides the added advantage ofmaterial information in addition to high resolution distancedetermination.

During use of the ion microscope systems for critical dimensionmeasurements, a flood gun can be used to prevent excessive charging ofthe sample surface (see discussion above). Alternatively oradditionally, very low He ion beam currents (e.g., 100 fA or less) canbe used. In addition to reducing surface charge and maintaining imagefidelity, the use of low ion currents reduces ion beam-induced damage tocertain resist materials.

In some embodiments, wafer samples selected for critical dimensionmeasurement may first need to be sectioned (e.g., to measure across-sectional dimension of the sample). For this purpose, heaviergases such as Ne and Ar can be used in the ion microscope to form an ionbeam which can be used to slice through the sample. Alternatively, aGa-based FIB can be used to section the sample. Then, the microscopesystem can be purged of these gases and He can be introduced, so thatcritical dimension measurements are made with a He ion beam, avoidingsample damage during metrology.

(viii) Line Edge Roughness and Line Width Roughness

Line edge roughness generally refers to the roughness of the edge of aline of material in a semiconductor article, and line width roughnessgenerally refers to the roughness of the width of a line of material ina semiconductor article. It can be desirable to understand these valuesto determine whether actual or potential problems exist in a givensemiconductor article. For example, if adjacent lines formed ofelectrically conductive material have edges that bulge outward towardeach other, the lines may contact each other resulting in a short. Itcan be desirable to understand the dimensions of line edge roughnessand/or line width roughness to within five nm or less (e.g., four nm orless, three nm or less, two nm or less, one nm or less, 0.9 nm or less,0.8 nm or less, 0.7 nm or less, 0.6 nm or less, 0.5 nm or less). In someembodiments, the line edge roughness and/or line edge width is measuredmultiple times to provide statistical information regarding the size ofthe feature. In addition, fabrication tolerances for parameters such asline edge roughness can be very high. For example, line edge roughnessof semiconductor article features may have to be controlled within 5 nmor less (e.g., within 4 nm or less, within 3 nm or less, within two nmor less, within one nm or less, within 0.5 nm or less, within 0.1 nm orless, within 0.05 nm or less, within 0.01 nm or less).

When determining line edge roughness and line width roughness, wafersmay be selected at random from a fabrication line for inspection, or allwafers on the line can be inspected. An imaging instrument can be usedto measure line edge roughness and line width roughness at a relativelyhigh throughput rate. If the measured line edge roughness and line widthroughness does not fall within acceptable limits, the wafer may bediscarded. If multiple samples originating from a particular fabricationmachine have line edge roughness and line width roughness outsideacceptable limits, the machine may be taken out of service, or itsoperating parameters may be changed.

The gas field ion microscope (e.g., He ion microscope) disclosed hereincan be used for metrology of line edge roughness and line widthroughness. In particular, the He ion beam can be raster-scanned alongthe length of a feature, and the resulting information can be used todetermine the line edge roughness and line width roughness withrelatively high precision.

With regard to line edge roughness and line width roughness measurement,He ion microscope systems can provide a number of advantages relative toSEMs and other inspection systems. He ion microscope images generallyexhibit less edge blooming (generally, excessive signal, approaching thepoint of saturation of the detector, due to enhanced yield attopographic features with slopes nearly parallel to the beam) thancomparable SEM images. The reduced edge blooming is a result of thesmaller interaction volume between He ions and the surface of thesample, relative to the interaction volume of electrons with thesurface.

In addition, the incident He ions can be focused to a smaller spot sizethan a comparable incident electron beam. The smaller beam spot size, incombination with the smaller interaction volume, results in images ofthe sample having resolution that is superior to images produced withSEMs, and more accurate determination of line edge roughnesses and linewidth roughnesses of samples.

The depth of focus of a He ion beam is relatively large compared to aSEM. As a result, the resolution of sample features at varying depths ismore consistent when using an ion beam, as compared to an electron beam.Therefore, using an ion beam can provide information at various sampledepths with better and more consistent lateral resolution than can beprovided using an electron beam. As an example, better line widthprofiles than can be achieved using an ion beam than can be achievedwith an electron beam.

Further, in embodiments in which information is obtained based at leastin part on secondary electrons, the relatively high yield of secondaryelectrons provided by an ion beam, as compared to an electron beam, canresult in a relatively high signal to noise ratio for a given current.This can, in turn, allow for sufficient information about the sample tobe obtained in a relatively short period of time, increasing throughputfor a given current.

Imaging of the samples for determination of critical dimensions can beperformed using scattered He ions. This provides the added advantage ofmaterial information in addition to high resolution distancedetermination.

During use of the ion microscope systems for line edge roughness andline width roughness measurements, a flood gun can be used to preventexcessive charging of the sample surface (see discussion above).Alternatively or additionally, very low He ion beam currents (e.g., 100fA or less) can be used. In addition to reducing surface charge andmaintaining image fidelity, the use of low ion currents reduces ionbeam-induced damage to certain resist materials.

In some embodiments, wafer samples selected for line edge roughness andline width roughness measurement may first need to be sectioned (e.g.,to measure a cross-sectional dimension of the sample). For this purpose,heavier gases such as Ne and Ar can interact with a gas field ion sourceto generate an ion beam which can be used to slice through the sample.Then, the microscope system can be purged of these gases and He can beintroduced, so that critical dimension measurements are made with a Heion beam, avoiding sample damage during metrology.

(ix) Circuit Editing

As discussed previously, the process of forming a semiconductor articletypically involves stacking many different layers of material in adesired fashion, and performing appropriate processes on each layer.Generally, this involves depositing on and/or removing material from agiven layer. The final semiconductor article includes many differentfeatures in different layers (e.g., to form a desired circuit). Ingeneral, it is desirable for the features to be properly aligned for thefinal device to function as desired. Alignment marks are commonly usedin semiconductor articles to assist in properly aligning features in agiven layer with features in a different layer. However, using alignmentmarks can add extra steps to the overall fabrication process, and/or canintroduce other complexities or expenses to the fabrication process.Further, the mere presence of the alignment marks means that there areareas and/or volumes of the semiconductor article that are not availablefor use (e.g., for the fabrication of active components).

As noted above, an ion beam can be used to investigate the sub-surfaceregion of a material. This property can be used to determine thelocation of certain features in a layer beneath a surface layer,allowing features in different layers of the semiconductor article to bealigned as desired without the use alignment marks.

The gas field ion microscope (e.g., the He ion microscope) describedherein can be used to remove and/or deposit material (e.g., from anelectrical circuit) using, for example, the gas assisted chemistryand/or sputtering techniques noted above. An advantage of using an ionmicroscope to perform these processes is that the ion beam can also beused to assess the resulting product to determine, for example, whetherthe desired material was properly deposited or removed. This can reducethe cost and/or complexity associated with device fabrication, and/orincrease the throughput of device fabrication. Removal and/or additionof material capabilities can be combined to perform sub-surface circuitrepair. To repair a sub-surface defect, material from the device isfirst removed down to a depth that exposes the defect. The defect isthen repaired by either adding or removing material from the device.Finally, the overlying layers of the device are repaired,layer-by-layer, by adding appropriate thicknesses of new material.

The gas field ion microscope (e.g., the He ion microscope) describedherein can provide particular advantages for circuit editingapplications including small spot sizes and low ion currents forcontrolled and highly accurate editing of fabricated devices.

(x) Mask Repair

Semiconductor articles are typically prepared using a lithographyprocess that involves putting a layer of photoresist (e.g., polymerphotoresist, such as poly(methyl methacrylate) (PMMA) or epoxy-basedphotoresists, allyl diglycol carbonate, or photosensitive glasses) on asurface, patterning the material so that certain regions of thephotoresist are resistant to an etchant (and some regions are notresistant to an etchant), etching the non-etch resist regions of thematerial, depositing appropriate materials (e.g., one or moreelectrically conductive materials, one or more non-electricallyconductive materials, one or more semiconductive materials), andoptionally removing undesired regions of material. Typically, thepatterning step involves exposing the photoresist to a radiation patternof an appropriate wavelength so that some regions of the photoresist areetch resistant and other regions of the photoresist are not etchresistant. The radiation pattern can be formed on the photoresist byforming an image of a mask onto the photoresist or covering certainregions of the photoresist with a mask, and exposing the uncoveredregions of the photoresist through the mask.

Photolithographic masks used to fabricated integrated circuits and othermicroelectronic devices in the semiconductor industry can be fragileand/or expensive. In addition, mask fabrication processes can betime-consuming and/or delicate. In some circumstances, despite the carewhich is typically used during the manufacturing of such masks,fabrication errors produce mask defects. In other circumstances, maskdefects can arise from handling and general use. If circuits or otherdevices were produced using the defective masks, the circuits or devicesmay not operate correctly. Given the time and expense required tofabricate a new mask, it may be more cost-effective to edit a defectivemask than to fabricate an entirely new mask.

Mask defects generally include an excess of mask material in a region ofthe mask where there should be no material, and/or an absence of maskmaterial where material should be present. In either situation, the gasfield ion microscope (e.g., the He ion microscope) described herein maybe used to inspect and/or repair a mask.

In some embodiments, the gas field ion microscope (e.g., He ionmicroscope) disclosed herein can be used to inspect the mask todetermine whether a defect and present, and, if a defect is present,where the defect is. Many of the various advantageous featured providedby the gas field ion microscope (e.g., He ion microscope) disclosedherein are desirably used to image the mask.

In certain embodiments, in addition to imaging the mask during maskrepair, the gas field ion microscope (e.g., He ion microscope) can beused during the repair process. As an example, the gas field ionmicroscope can be used to position the mask relative to a FIB so thatthe FIB can be used to add and/or remove material from the mask usinggas surface chemistry process and/or etching processes, such asdescribed above. As another example, the gas field ion microscope, inaddition to initially imaging the mask to determine the existence and/orlocation of a defect, can be used to add and/or remove material from themask using gas surface chemistry process and/or etching processes, suchas described above. Optionally, the gas field ion microscope can be usedto conduct certain repair steps (add material, remove material) whileanother instrument (e.g., a FIB) is used to conduct other repair steps(add material, remove material).

(xi) Defect Inspection

In general, during the process of fabricating a semiconductor article,the article is inspected for potential defects. Typically, theinspection is performed using an in-line tool which is always runningand being fed wafers and that is fully automatic. The tool is often usedto examine a small area of wafer whether there are regions where adefect will occur. This inspection is performed prior to defect review(see discussion below). The goal of defect inspection typically is todetermine whether a defect may exist, as opposed to determining theexact nature of a given defect. During defect inspection, a region of awafer is analyzed to see whether certain anomalous properties (e.g.,voltage contrast properties, topographical properties, materialproperties) are exhibited by the sample, relative to other regions ofthe same wafer and/or to regions of other wafers. Typically, for apotential defect, the coordinates (e.g., X,Y coordinates) on the waferare noted, and the location of the wafer is more carefully inspectedduring defect review.

A gas field ion microscope (e.g., a He ion beam) as described herein canbe used to gather information about a sample during defect inspection.Such a microscope can be used for relatively high throughput and highquality defect inspection. The different contrast mechanisms provided bythe gas field ion microscope (e.g., He ion microscope) can permitvisualization of different types of defects and at higher resolutionthan can generally be observed using optical imaging techniques.

(xii) Defect Review

In general, if a sample is noted as having a potential defect duringdefect inspection, that sample is then submitted to defect review wherethe particular region(s) of the sample having the potential defectis(are) investigated to determine the nature of the defect. Based onthis information, modifications to the process may be implemented toreduce the risk of defects in final product. Typically, defectinspection is conducted at slower speed and higher magnification thandefect review, and may be automated or conducted manually to obtainspecific information regarding one or more defects. The information isused to attempt to understand why anomalous results were obtained duringdefect review, and the nature and cause of the defects that gave rise tothe anomalous results.

The gas field ion microscope (e.g., He ion microscope) described hereincan be used to investigate a semiconductor article at various steps(e.g., each step) in the fabrication process. In particular, bydetecting and analyzing one type of particle or multiple different typesof particles (see discussion above), the gas field ion microscope (e.g.,He ion microscope) can be used to determine topographical informationabout the surface of the semiconductor article, material constituentinformation of the surface of the semiconductor article, materialconstituent information about the sub-surface region of thesemiconductor article, crystalline information about the semiconductorarticle, voltage contrast information about the surface of thesemiconductor article, voltage contrast information about a sub-surfaceregion of the semiconductor article, magnetic information about thesemiconductor article, and/or optical information about thesemiconductor article. The different contrast mechanisms provided by theHe ion microscope can permit visualization of defects that wouldotherwise not appear using SEM-based techniques.

Using an ion microscope or ion beam as described herein can provide avariety of different advantages, which, in general, can reduce the time,cost and/or complexity associated with semiconductor articlefabrication. Exemplary advantages associated with using the ionmicroscope or ion beam described herein include relatively highresolution, relatively small spot size, relatively little undesirablesample damage, relatively little undesirable material deposition and/orimplantation, relatively high quality imaging in a relatively short timeperiod, relatively high throughput.

(xiii) Circuit Testing

During the fabrication of a semiconductor article, the electricalconductivity and functionality of one or more features of the articlemay be tested. This process generally involves exposing the feature(s)to charged particles and then monitoring the rate at which the charge isaccumulated. An open circuit will charge at a different rate relative toa closed circuit, allowing an open circuit to be identified andconsidered for more detailed inspection. A gas field ion microscope(e.g., a He ion microscope) as described herein may be used to apply thecharge to the feature using the ion beam, and/or may be used to monitorwhether the charge has leaked away (e.g., by monitoring the voltagecontrast characteristics). Optionally, a flood gun can be used to applythe charge (see discussion above), and the gas field ion microscope canbe used to monitor whether the charge has leaked away (e.g., bymonitoring the voltage contrast characteristics).

B. Metal and Alloy Corrosion

He ion microscopes can be used to identify and examine metal corrosionin various devices and material. For example, metal fixtures and devicesused in nuclear power plants, military applications, and biomedicalapplications can undergo corrosion due to the harsh environments inwhich they are deployed. He ion microscopes can be used to constructimages of these and other devices based on the relative abundance ofhydrogen (H) in the devices, which serves as reliable indicator ofcorrosion.

Typically, to construct images based on scattered H ions or atoms, adetector for these ions or atoms is positioned on the back side of asample, opposite to an incident He ion beam. Exposing the sample to Heions generates scattered H atoms and ions from within the sample, andthese scattered H atoms and ions can be detected and used to constructimages of the sample. The H abundance images can then be used to assessthe extent of corrosion within the sample. The small spot size andinteraction volume of the He ion beam can result in high resolution Himages of the sample to be obtained without damaging the sample.

C. Read/Write Structures for Data Storage

Read/write heads used in magnetic storage devices such as hard disks arefabricated to extremely high tolerances and must be inspected formanufacturing defects prior to installation. These devices frequentlyhave very high aspect ratios; the short sides of such devices can be assmall as 1 nm. He ion microscopes provide numerous advantages when usedto image these devices during inspection. Among these are small spotsizes and interaction volumes, which can result in high resolutionimaging of these tiny devices, a large depth of focus, which can allowin-focus imaging of the entire high-aspect-ratio device along its longdimension, and material information provided by measurement of scatteredHe ions and/or neutral atoms, which is used to verify that tiny circuitelements are properly connected.

D. Biotechnology

It is often desirable to determine elemental and/or chemicalcompositional information about a biological sample using anon-destructive technique. Examples of biological samples includetissue, nucleic acids, proteins, carbohydrates, lipids and cellmembranes.

A gas field ion microscope (e.g., a He ion microscope) as describedherein can be used to determine, for example, topographical informationabout a biological sample, material constituent information of a surfaceof a biological sample, material constituent information about thesub-surface region of a biological sample and/or crystalline informationabout a biological sample. For example, the gas field ion microscope canbe used to image immuno-labeled cells and internal cell structures. Themicroscope can be used in this manner while providing certain advantagesdisclosed herein.

E. Pharmaceutical

Often, a therapeutic agent (e.g., small molecule drug) will form as acrystal (e.g., as it comes out of solution). It can be desirable todetermine the crystalline structure of the crystallized small moleculebecause this can, for example, provide information regarding the degreeof hydration of the small molecule, which, in turn, can provideinformation regarding the bioavailability of the small molecule. Incertain instances, the crystalline information may turn out todemonstrate that the small molecule is actually in an amorphous (asopposed to crystalline) form, which can also impact the bioavailabilityof the small molecule.

Additionally or alternatively, it is often desirable to determineelemental and/or chemical compositional information about a biologicalsample using a non-destructive technique.

A gas field ion microscope (e.g., a He ion microscope) as describedherein can be used to determine, for example, topographical informationabout a biological sample, material constituent information of a surfaceof a biological sample, material constituent information about thesub-surface region of a biological sample and/or crystalline informationabout a biological sample. The microscope can be used in this mannerwhile providing certain advantages disclosed herein.

Computer Hardware and Software

In general, any of the analysis methods described above can beimplemented in computer hardware or software, or a combination of both.The methods can be implemented in computer programs using standardprogramming techniques following the methods and figures describedherein. Program code is applied to input data to perform the functionsdescribed herein and generate output information. The output informationis applied to one or more output devices such as a display monitor. Eachprogram may be implemented in a high level procedural or object orientedprogramming language to communicate with a computer system. However, theprograms can be implemented in assembly or machine language, if desired.In any case, the language can be a compiled or interpreted language.Moreover, the program can run on dedicated integrated circuitspreprogrammed for that purpose.

Each such computer program is preferably stored on a storage medium ordevice (e.g., ROM or magnetic diskette) readable by a general or specialpurpose programmable computer, for configuring and operating thecomputer when the storage media or device is read by the computer toperform the procedures described herein. The computer program can alsoreside in cache or main memory during program execution. The analysismethods can also be implemented as a computer-readable storage medium,configured with a computer program, where the storage medium soconfigured causes a computer to operate in a specific and predefinedmanner to perform the functions described herein.

OTHER EMBODIMENTS

While certain embodiments have been described, other embodiments arepossible.

As an example, a SEM can be used in one or more of the precedingembodiments in combination with a gas field ion microscope. For example,a SEM can be used to produce secondary electrons, Auger electrons, X-rayphotons, IR photons, visible photons and/or UV photons. Optionally, aSEM can be used to promote gas assisted chemistry. The gas field ionmicroscope can be configured in any of the operating modes disclosedherein, so that the SEM and the gas field ion microscope performcomplementary functions.

As another example, while a W(111) tip has been disclosed, differentcrystallographic orientations of W can also be used in a tip. Forexample, a W(112), W(110) or W(100) tip may be used.

As a further example, in some embodiments, the ion microscope (e.g., gasfield ion microscope) can include appropriate componentry to allow themicroscope to be used in-line for the analysis of samples, such assamples relevant to the semiconductor industry (e.g., wafer samples). Incertain embodiments, for example, the ion microscope may be automatedwith a high-speed loadlock for standard sized semiconductor wafers. Insome embodiments, the system may include a wafer stage capable ofputting a portion of a sample wafer under the ion microscope at highspeed. The ion microscope may also include a scan system capable ofhigh-speed rastering of metrology patterns. Optionally, the ionmicroscope may also include a charge neutralization scheme to reducesample charging. The ion microscope may also include a wafer heightcontrol module for adjusting working distances. In certain embodiments,the system may be configured so that individual dies (e.g., havinglengths on the order of 50 mm) can be imaged.

EXAMPLES

The following examples are illustrative and not intended as limiting.

1

A 25 mm length of emitter wire formed of single crystal W(111) (diameter250 μm) was obtained from FEI Company (Hillsboro, Oreg.). The emitterwire was trimmed to a 3 mm length and set aside. A V-shaped heater wirewas prepared as follows. A 13 mm length of polycrystalline tungsten wire(diameter 180 μm) was obtained from Goodfellow (Devon, Pa.) and cleanedby sonication for 15 minutes in distilled water to remove the carbonresidue and other impurities. The wire was bent at its midpoint to forman angle of 115 degrees. The region near the apex of the “V” waselectrochemically etched to prepare it for welding in a 1N aqueoussolution of sodium hydroxide (NaOH) with an applied AC potential of 1 Vand frequency 60 Hz for a duration of approximately 15 seconds. Theheater wire was then removed from the etching solution, rinsed withdistilled water, and dried.

The V-shaped heater wire was mounted in a fixture to ensure that theends of the wire remained coplanar. The emitter wire was spot welded tothe V-shaped apex of the heater wire. Then, the two ends of the heaterwire were spot welded to two posts of a support base of the type shownin FIGS. 11A and 11B. The support base was obtained from AEI Corporation(Irvine, Calif.). The resulting assembly was then cleaned ultrasonicallyin distilled water and dried.

Following mounting of the emitter wire on the support base and cleaningof the support base, the end of the emitter wire was etched by anelectrochemical process as follows. First, a resist material (e.g., nailpolish obtained from Revlon Corporation, New York, N.Y.) was applied toa 0.5 mm length of the emitter wire, starting from the free end of thewire. A drop of resist was placed on the surface of a clean glassmicroscope slide, and the wire was dipped ten times into the resistsolution, allowing the resist to dry slightly between each dipping. Carewas taken to assure that the upper boundary of the resist was in theshape of a circle, and that the plane of the circle was maintainedperpendicular to the axis of the wire. Following the last dip of the endof the emitter wire into the resist material, the wire was allowed todry for 1 hour in air.

The support base with the resist-coated emitter wire attached was thenattached to an etching fixture that included: (a) a translationapparatus for vertically translating the support base; (b) a dish; and(c) a counter electrode, formed of stainless steel to minimize undesiredchemical reactions, that extended into the dish. The dish was filledwith an etching solution to a level such that the solution was incontact with the counter electrode. Approximately 150 mL of solution waspresent in the etching fixture dish. The orientation of the support basewas adjusted to ensure that the longitudinal axis of the emitter wirewas approximately parallel to the vertical direction (e.g., thedirection along which the translation apparatus provided for translationof the support base). Then, the support base was lowered toward the dishusing the translation apparatus until the exposed emitter wire justcontacted the etching solution. A high magnification camera mounted tothe etching fixture allowed the resist layer and etching solutionsurface to be seen easily, and permitted accurate positioning of theemitter wire with respect to the solution surface.

Then, the wire was lowered an additional 0.2 mm into the etchingsolution. In this position, the resist coated portion of the emitterwire was fully immersed in etching solution.

The etching solution consisted of 150 mL of 2.5 M aqueous NaOH. Tofacilitate wetting, 1 drop of surfactant (PhotoFlo 200, obtained fromEastman Kodak, Rochester, N.Y.) was added to the etching solution.Gentle stirring of the etching solution using a magnetic stirrer wasalso employed during the etching process.

An external power supply was connected to the support base posts and thecounter electrode. The voltage maximum amplitude, pulse duration, andwaveform shape of the external power supply could be controlled toprovide particular etching conditions in the etching fixture.

A sequence of AC pulses at a frequency of 60 Hz was applied to theemitter wire to facilitate the electrochemical etching process. First,one hundred pulses of duration 580 ms and amplitude 10 V were appliedover a total time window of 5 minutes. The effect of the applied pulseswas to increase the rate of the etching process. Portions of the emitterwire which were immersed in solution but not covered by resist materialbegan to etch away. Because the emitter wire was positioned so that onlya small uncoated region of the wire above the edge of the photoresistmaterial was immersed in solution, localized etching of the emitter wirein this region was observed. As the electrochemical reaction proceeded,the diameter of the wire in this region began to get narrower due to theetching process.

Next, the pulse duration of the external power supply was adjusted to325 ms, and sixty pulses of this duration were applied to the emitterwire over a total time window of 5 minutes. These pulses furtherpromoted the electrochemical etching process, resulting in an etchedregion of the emitter wire with a very small diameter.

Finally, the pulse duration of the external power supply was adjusted to35 ms, and individual pulses were applied to the emitter wire untiletching was complete and the resist-coated portion of the emitter wiredropped off into the etching solution. The support base was then removedfrom the etching fixture, rinsed with distilled water, and dried under aflow of nitrogen.

The emitter wire—still attached to the support base—was then examinedusing a SEM to verify that the etched tip had suitable geometricalfeatures. An AMRAY Model 1860 SEM operating at 5 keV and with a probesize of 3 nm was used to image the emitter wire tip. The support basewas installed in a sample region of the SEM, on a sample manipulatorequipped with a tilt and rotate manual stage. Images of the source wereacquired from several different observation perspectives andmagnifications to verify that the tip was approximately correctlyshaped.

The SEM images were then used to characterize the average full coneangle, the average tip radius, and average cone direction, as discussedpreviously of the apex of the tip of the wire. The images used for thesemeasurements were taken at a magnification of 65,000×, and along aviewing axis oriented at right angles to the axis of the emitter wire.The emitter wire tilt was adjusted using the SEM sample manipulator toensure that the emitter wire was oriented orthogonally with respect tothe viewing axis. To make average measurements of the tip's cone angle,cone direction, and radius, the SEM sample manipulator was used torotate the tip by 45° (about the axis of the emitter wire) betweensuccessive images. This yielded a set of eight images of the tip—eachfrom a different perspective—which were then used to determine the coneangle, radius of curvature, and cone direction of the tip.

Four of the eight perspective images are shown in FIGS. 37A-37D. Each ofthe SEM images was digitized into bitmap format and then analyzed usingcustom algorithms developed using the MathCAD software package (PTCInc., Needham, Mass.). First, each of the images was smoothed byapplying a Gaussian convolution algorithm to reduce image noise,particularly noise due to vibrations of the SEM that occurred duringimaging. A filtering step based upon a threshold intensity value wasthen applied to each of the images to emphasize the boundary between thetungsten tip and the black background. The tip boundary in each imagewas then determined as the set of nonzero-intensity (X,Y) points thatformed a demarcation between image pixels corresponding to the tip andimage pixels corresponding to the black (e.g., zero-intensity)background. One such set of (X,Y) points for one of the views of the tipis shown in FIG. 38. Similar sets of boundary points were determined foreach of the eight perspective views of the tip.

Prior to calculating the slope of a given boundary curve, a smoothingalgorithm was applied to the curve to ensure that the local slope of thecurve was relatively insensitive to noise and other small signalvariations. The smoothing algorithm consisted of fitting the raw (X,Y)data points to a fourth-order polynomial, which has been found todescribe the shape of the tip well. The effect of the smoothingalgorithm was to ensure that, on either side of the apex position, thefirst derivative of this curve is not excessively influenced by smallvariations in the shape.

Following the smoothing step, the slope dY/dX was calculated at each Xpoint along the boundary curves for each view using a finite differencealgorithm. FIG. 39 shows a graph of the calculated slope at points alongthe boundary curve as a function of X for the boundary curve shown inFIG. 38.

For a particular view of the tip, the position on the boundary curvecorresponding to that view where the slope acquired a zero value wasidentified as the tip apex and given the label X_(apex). The position onthe boundary curve corresponding to the (X,Y) point, closest to the tipapex, where the slope of the boundary curve acquired a value of 1 wasgiven the label X₊₁. The position on the boundary curve corresponding tothe (X,Y) point, closest to the tip apex, where the slope of theboundary curve acquired a value of −1 was given the label X⁻¹.

These measured points were then used to determine geometrical parametersof the tip. The left radius of the tip in a particular view wascalculated as the absolute value of the difference between X₊₁ andX_(apex), multiplied by 1.414. The right radius of the tip in aparticular view was calculated as the absolute value of the differencebetween X⁻¹ and X_(apex), multiplied by 1.414. Then, based on the leftand right radius values, the radius of curvature of the tip in aparticular view was calculated as the average of the left radius and theright radius values.

The calculations of the right radius, left radius, and tip radius ofcurvature were repeated for each of the eight perspective views of thetip. The average tip radius was then calculated as the average of thetip radius of curvature measurements in all of the views of the tip. Forthe tip shown in FIGS. 37A-37D, the average tip radius was determined tobe 62 nm.

The standard deviation of all of the tip left and right radii was alsocalculated, and expressed as a percentage of the average tip radius. Forthe tip shown in FIGS. 37A-37D, the eccentricity was determined to be11.9%.

The cone angle of the tip in each of the eight perspective views wasalso determined. In the boundary curve corresponding to each view, leftand right tangent points on the boundary curve were located on the leftand right sides of the tip apex, respectively, at positions 1 μm fromthe tip apex, measured along the Y direction, as discussed previously.The left cone angle of the tip in a particular view was then determinedas the angle between a tangent to the boundary curve at the left tangentpoint and a line parallel to the Y axis and extending through the lefttangent point. The right cone angle of the tip in a particular view wasdetermined as the angle between a tangent to the boundary curve at theright tangent point and a line parallel to the Y axis and extendingthrough the right tangent point. Finally, the full cone angle wasdetermined as the sum of the magnitudes of the left and right coneangles.

The average full cone angle of the tip was then determined bycalculating the average of the eight measurements of the full cone angleof the tip from the eight perspective views of the tip. For the tipshown in FIGS. 37A-37D, for example, the average full cone angle wasdetermined to be 34.5°.

For a particular view of the tip, the cone direction was calculated asthe half of the absolute value of the difference between the magnitudesof the left and right cone angles. Repeating this determination for eachof the eight views of the tip yielded eight measurements of the conedirection of the tip. The average cone direction of the tip was thencalculated as the average of these eight measurements of the conedirection. For the tip shown in FIGS. 37A-37B, the average conedirection was determined to be 2.1°.

A set of criteria based on the measurements of average tip radius,radius eccentricity, average cone angle, and average cone direction wereused to determine whether a given tip would be accepted for use in theHe ion microscope. In general, these criteria were as follows. The tipwas accepted for use if the measured average cone angle was between 15°and 45°, the average tip radius was between 35 nm and 110 nm, thestandard deviation of the tip radius of curvature measurements was lessthan 30%, and the average cone direction was less than 7°. Ultimately,the tip shown in FIGS. 37A-37D satisfied each of these criteria, and sothis tip was accepted for use in the He ion microscope.

After verification of the tip geometrical properties, the tip wasinspected in a custom-built FIM. The FIM included a mounting area forthe support assembly supporting the tip, a high voltage power supply forbiasing the tip, an extractor adjacent to the tip, and a detector forrecording ion emission patterns from the tip.

The extractor was spaced from the tip by a distance of 5 mm and had anopening of 10 mm. The extractor was grounded to an external ground. Thedetector, a combination microchannel plate (MCP) and image intensifier(obtained from Burle Electro-Optics Inc., Sturbridge, Mass.) waspositioned at a distance of 75 mm from the extractor.

The support assembly including the tip was installed in the FIM and theFIM chamber was evacuated to a background pressure of 1×10⁻⁸ Torr. Thetip was cooled to 77 K using liquid nitrogen as a coolant. Aftertemperature equilibration, the source was heated to 900 K for 5 minutesto desorb condensates or other impurities that had formed on the tipduring processing. Heating of the tip was accomplished by applying anelectrical current to the heater wire to which the tip was welded. Thecurrent was applied using a power supply with constant powercapabilities (Bertan Model IB-30A, available from Spellman High VoltageInc., Hauppauge, N.Y.). Temperature measurements were made using anoptical pyrometer (obtained from Pyro Corporation, Windsor, N.J.).

Subsequently, the tip was then allowed to cool again to 77 K, and theFIM extractor was grounded and the tip was biased to +5 kV relative tothe extractor. High purity He gas (99.9999% pure) was introduced intothe FIM chamber at a pressure of 1×10⁻⁵ Torr. The tip bias wasprogressively increased to +29 kV in increments until a He ion imagecorresponding to He ions leaving the tip was observed on the detector.The FIM emission pattern corresponded to about 300 atoms on the surfaceof the tip. Based on the FIM pattern, the single crystal composition andW(111) orientation of the tip were verified.

Next, the tip was sharpened to obtain a terminal atomic trimer at thetip apex. Helium gas was pumped out of the FIM chamber until thebackground pressure in the chamber was less than 1.2×10⁻⁸ Torr. The tipwas then heated, via application of current to the heater wires asdescribed above, to a temperature of 1500 K for 2 minutes. Oxygen gaswas introduced into the FIM chamber in the vicinity of the tip at apressure of 1×10⁻⁵ Torr. After 2 minutes, the tip temperature wasreduced to 1100 K. After 2 minutes at 1100 K, the oxygen supply was shutoff and the tip was allowed to cool to approximately 77 K. Duringcooling, and about 15 minutes after the oxygen supply was shut off, theresidual oxygen gas was pumped out of the FIM chamber until thebackground pressure in the chamber was less than 1.2×10⁻⁸ Torr.

Once cooled to liquid nitrogen temperature, the extractor was biased asabove, and the tip was again biased at +5 kV relative to the extractor.He gas at a pressure of 1×10⁻⁵ Torr was introduced into the FIM chamber,and the FIM was once again operated as described above to acquire Heemission images of the tip. The tip voltage was progressively increaseduntil a FIM image of the tip was captured by the detector at a biaspotential of about +18 kV on the tip.

The observed FIM pattern included adatoms—extra atoms in addition to thedesired three atom trimer structure at the tip apex. The adatoms wereslowly removed by field evaporation at the tip bias potential of +18 kV.During field evaporation, images of the tip were captured periodicallyand monitored to determine when to halt the field evaporation process.The adatoms were removed one by one until a clear FIM image of an atomictrimer at the tip apex was observed. In addition to the atomic trimer,the ridges of a 3 sided pyramid were also clearly observed.

The atomic trimer was slowly removed by further field evaporation of thetip. By increasing the tip bias slowly beyond +18 kV, the trimer atomswere removed one by one, resulting in rounded tip that was observed inFIM images recorded by the detector.

The tip bias potential was further increased up to +28 kV. Fieldevaporation of the tip atoms continued during this process. At a biaspotential of +28 kV, another atomic trimer was obtained at the apex ofthe tip. A FIM image of the second trimer is shown in FIG. 40. After thesecond trimer was obtained, the tip bias potential was reduced to attainthe highest angular intensity in the FIM emission pattern. This occurredat a tip bias of +23 kV. The highest angular intensity was determined byadjusting the tip bias to obtain the largest observed brightness of aselected atom in the FIM emission pattern. The bias at which the highestangular emission intensity occurred was verified by measuring the He ioncurrent from the trimer as the potential bias of the tip was adjusted.The He ion current was measured using a Faraday cup positioned in thepath of the He ion beam.

The tip was then blunted to a nearly spherical end-shape by slowlyincreasing the bias potential of the tip above +28 kV and fieldevaporating atoms from the tip apex. Field evaporation was continueduntil another atomic trimer was obtained at the surface of the tip at abias potential of +34 kV. To verify the repeatability of the tipre-building procedure, the sharpening process was repeated twice more toobtain new atomic trimers at the tip apex. After two successive trimerre-builds, the Helium gas supply was shut off, the applied tip bias wasremoved, the tip was allowed to warm to room temperature, and the FIMchamber pressure was slowly equalized to atmospheric pressure. The tip,still mounted in the support assembly, was stored on a shelf for aperiod of 2 weeks until it was used in a helium ion microscope.

The support assembly including the tip was installed in a helium ionmicroscope system similar to the system shown in FIGS. 1 and 5. Theelements of the system were configured as follows. The extractor waspositioned 1 mm from the tip, and had an opening of diameter 3 mm. Thefirst lens of the ion optics was positioned at a distance 30 mm from theextractor. After passing through the first lens, ions passed through thealignment deflectors, which were configured as quadrupole electrodes. Anaperture with an opening of diameter of 20 μm was positioned furtheralong the path of the ions to selectively block a portion of the ionbeam. A cross-over point of the ion trajectories was positioned at adistance of 50 mm in front of the aperture. The astigmatism corrector,configured as an octupole electrode, was positioned after the apertureto adjust astigmatism of the ion beam. Scanning deflectors, configuredas octupole electrodes, were positioned after the astigmatism correctorto permit rastering of the ion beam across the surface of a sample. Thesecond lens was positioned at a distance 150 mm from the aperture, andwas used to focus the ion beam onto the surface of a sample. The secondlens was shaped as a truncated right-angled cone, with a full cone angleof 90°.

Initially, the ion microscope system was evacuated so that the basepressure in the tip area was about 2×10⁻⁹ Torr. The tip was cooled toabout 80 K using liquid nitrogen. The extractor was grounded, and a biasof +5 kV, relative to the extractor, was then applied to the tip.

The tip was heated by applying electrical power of 8 W to the heaterwire, until it was visibly glowing (corresponding to a tip temperatureof about 1100 K). Photons emitted from the glowing tip were observedfrom a side port of the ion optics, using a mirror tilted at 45° withrespect to a plane perpendicular to the longitudinal axis of the ionoptics. The mirror was introduced for this purpose into the ion optics,in a position just below the alignment deflectors, via a side port inthe ion column. The tip was tilted and shifted iteratively until theglowing tip was aimed roughly along the longitudinal axis of the ionoptics. Proper alignment of the tip with the longitudinal axis wasachieved when the glowing tip appeared as a circular point source. Thetip was misaligned if it appeared to be rod-shaped.

The tip was allowed to cool while maintaining the tip at a potentialbias of +5 kV relative to the extractor. Once the tip had cooled toliquid nitrogen temperature, He gas was introduced into the tip regionat a pressure of 1×10⁻⁵ Torr. The ion microscope system was run in SFIMmode, as described above, to generate an image showing the He ionemission pattern of the tip. The image indicated the shape of the tip toatomic precision. The alignment electrodes were used to raster the ionbeam generated from the tip over the surface of the aperture. Sawtoothvoltage functions were applied to each of the alignment deflectors toachieve rastering at a frame rate of 10 Hz, with a maximum voltage ofthe sawtooth functions of 150 V relative to the common external groundof the microscope system. The raster pattern scanned 256 points in eachof two orthogonal directions transverse to the axis of the ion optics.The astigmatism corrector and the scanning deflectors were not used inthis imaging mode.

To detect the ions that passed through the aperture, a sample of copperwas placed under the second lens, and a MCP detector was positivelybiased (+300 V relative to the common external ground) to measuresecondary electrons that left the copper sample due to the interactionbetween the sample and the He ions incident on the sample. The detectorwas positioned at a distance of 10 mm from the sample and orientedparallel to the plane of the sample.

The acquisition system sampled the detector signal at each raster pointand generated a SFIM image of the tip, which was displayed on a monitor.To facilitate imaging, the potential of the first lens in the ion columnwas set to be 77% of the tip bias. Then, as the tip bias was increased,the SFIM image was maintained with roughly constant magnification andintensity. While observing the SFIM image, the tip bias was slowlyincreased to eliminate undesired adatoms and to produce a tip with anatomic trimer at its apex. This trimer was removed by further increasingthe tip bias potential to cause field evaporation of the tip atoms.Field evaporation continued until a new atomic trimer was formed on theapex of the tip at an applied tip potential of +23 kV. The resultingSFIM image of this tip is shown in FIG. 41.

With the alignment deflectors, astigmatism corrector, scanningdeflectors, and second lens off (e.g., at zero potential relative to thecommon external ground of the microscope system), one atom of the trimerwas selected and the tip was tilted and translated while the strength ofthe first lens was modulated by 100 V. The microscope system wasoperated in FIM mode and the detector collected FIM emission images ofthe tip. The tip was tilted and translated iteratively until theposition of the center of the tip on the FIM images was unchanged fromone image to another when the strength of the first lens was modulated.

Next, the aperture was put in place and the potentials applied to thealignment deflectors were adjusted to control the position of the ionbeam at the aperture. The portion of the ion beam transmitted throughthe aperture was imaged by the detector, and the detector images wereused to iteratively adjust the alignment deflectors.

The scanning deflectors were used to raster the ion beam transmittedthrough the aperture over the surface of the sample. A recognizable,high contrast feature (a copper grid) on the surface of the sample (partnumber 02299C-AB, obtained from Structure Probe International, WestChester, Pa.) was placed in the path of the ion beam under the secondlens, and secondary electron images of the feature were measured by thedetector using the configuration discussed above.

The strength of the second lens was adjusted to roughly focus the ionbeam on the sample surface; the potential bias applied to the secondlens was about 15 kV, relative to the common external ground. Thequality of the focus was assessed visually from the images of the samplerecorded by the detector. The alignment of the ion beam with respect tothe axis of the second lens was evaluated by slowly modulating thestrength of the second lens—at a frequency of 1 Hz and an modulationamplitude of about 0.1% of the operating voltage of the second lens—andobserving the displacement of the feature. The beam alignment in thefinal lens was optimized by adjusting the voltages of the alignmentdeflectors. The alignment was optimized when the position of the centerof the image measured by the detector did not change significantlyduring modulation of the strength of the second lens.

Then, the sample was imaged at a higher magnification by adjusting thestrength of the second lens, so that the field of view on the sample wasabout 2 μm square. The asymmetry of the focus was minimized by adjustingthe astigmatism corrector controls. These controls were adjusted whileobserving the image and specifically the sharpness of edges in alldirections. The astigmatism correction was complete when the sharpnessof the focused image was the same in all directions. Typically, no morethan 30 volts were applied to the astigmatism corrector to achieve thiscondition. At this point, the helium ion microscope was fullyoperational.

The operational microscope was used to image a variety of samples.Sample images recorded by measuring secondary electrons are shown inFIGS. 42 and 43.

The imaging conditions included a wide range of beam currents (100 pA to1 fA). The beam current was controlled by several methods. First,different apertures with different diameter holes were put into positionusing a motorized aperture mechanism. The aperture mechanism includedapertures whose diameters ranged from 5 μm to 100 μm. Second, the firstlens focus strength was adjusted to move the beam crossover closer tothe aperture plane in the ion optics so that a larger ion currentreached the sample. Conversely, the first lens focus strength wasadjusted to move the beam further from the aperture plane so that lession current passed through the aperture. Third, the helium gas pressurein the tip region was increased or decreased to increase or decrease theion beam current, respectively.

The beam energy was typically selected for best angular intensity; thebeam energy was typically in a range from 17 keV to 30 keV. The beamenergy changed over time in response to the changing shape of the tip.

The type of detector used, and the detector's settings, were selectedaccording to the type of sample that was examined with the ionmicroscope. To measure secondary electron images of a sample, an ETdetector was used with a metal grid biased at about +300 V relative tothe common external ground. A scintillator internal to the ET detectorwas biased at +10 kV relative to the external ground, and the gain ofthe internal PMT adjusted to produce the largest possible signal withoutsaturation.

A MCP detector (obtained from Burle Electro-Optics, Sturbridge, Mass.)was also used to detect secondary electrons and/or scattered He fromsamples. The MCP grid, front face, and back face could each be biasedrelative to the external ground. The gain of the detector was attainedby biasing the back face of the MCP positive with respect to the frontend. Typical gain voltages were 1.5 kV. A collector plate adjacent tothe back face was biased at +50 V with respect to the back face. Fromthe collector plate, the detection signal was in the form of a smallvarying current which was superimposed on the large positive voltage.For collection of secondary electrons, the front face and grid of theMCP were biased to +300 V. For collection of scattered He, the frontface and grid were biased to −300 V.

The raster speed was adjusted as necessary for best imaging conditionsfor each sample. The dwell time per pixel ranged from 100 ns to 500 μs.For shorter dwell times, the noise was reduced by averaging multiplescans. This was done for successive line scans, and for successive framescans.

The image shown in FIG. 42 is an image of a plurality of carbonnanotubes on a silicon substrate. The image was acquired by detectingsecondary electrons from the surfaces of the nanotubes. An ET detectorwas positioned at a distance of 8 mm from the sample and 15 mm off-axisfrom the ion beam, and oriented at an angle of 20° with respect to theplane of the sample. The He ion beam current was 0.5 pA and the averageion energy was 21 keV. The ion beam was raster-scanned with a dwell timeof 200 μs per pixel, and the total image acquisition time was 200 s. Thefield of view of the image was 4 μm.

The image shown in FIG. 43 is an image of an aluminum post on a siliconsubstrate. The image was acquired by detecting secondary electrons fromthe surfaces of the nanotubes. A MCP detector of type described above,with the grid and front face biased at +300 V relative to the externalground, was positioned at a distance of 10 mm from the sample andoriented parallel to the plane of the sample. The He ion beam currentwas 0.5 pA and the average ion energy was 24 keV. The ion beam wasraster-scanned with a dwell time of 200 μs per pixel. The field of viewat the surface of the sample was 1 μm, obtained by applying a maximumvoltage of 1 V to the scanning deflectors.

Operation with this tip in the helium ion microscope continued for aperiod of weeks without any need to vent the system to service the ionsource. As trimer atoms were removed, either intentionally or throughnormal usage, the end form of the tip became more spherical, asindicated in the SFIM image shown in FIG. 44. In-situ pyramidre-building (sharpening) was performed as needed by using the same heatand oxygen build recipe as was performed originally in the FIM tosharpen the tip. In general, each rebuilding process consumed less than5 minutes of time, and the system was otherwise usable during thisperiod of weeks. Overall, the tip was rebuilt more than eight times. Animage of a rebuilt atomic trimer at the apex of the tip is shown in FIG.45.

2

A W(111) tip was mounted in a support assembly and electrochemicallyetched following the procedure described in Example 1. A SEM image ofthe tip is shown in FIG. 46. Geometrical characterization of the tip wasperformed according to the procedure in Example 1. For this tip, theaverage tip radius was determined to be 70 nm. The tip was accepted foruse based on the criteria in Example 1.

After verifying that the tip's geometrical properties were withinacceptable limits, the source assembly including the etched tip wasinstalled into the FIM described in Example 1. The configuration of theFIM was the same as the configuration discussed in Example 1, exceptwhere noted below. The potential bias on the tip, relative to theextractor, was slowly increased up to a potential of +21.8 kV. Fieldevaporation of tip atoms occurred as the potential was increased. Afterreaching +21.8 kV, the tip potential was reduced to +19.67 kV. The FIMimage of the tip shown in FIG. 47 was acquired with the tip maintainedat this potential. Using this image, the single crystal structure andcorrect orientation of the tip were verified.

Next, the tip was sharpened to produce an atomic trimer at the apex.Helium was pumped out of the FIM chamber, and the tip was heated byapplying a constant current of 4.3 A to the tip for 20 seconds. A tiltedmirror, installed in the FIM column and angled to re-direct lightpropagating along the column axis to a side port of the column, was usedto observed the tip. No glow (e.g., photons emitted from the tip) wasvisible to the eye, so the tip was allowed to cool for 5 minutes. Thenthe tip was heated by applying a constant current of 4.4 A to the tipfor 20 seconds. No glow was visible to the eye, so the tip was allowedto cool for 5 minutes. Then the tip was heated by applying a constantcurrent of 4.5 A to the tip for 20 seconds. No glow was visible to theeye, so the tip was allowed to cool for 5 minutes. Then the tip washeated by applying a constant current of 4.6 A to the tip for 20seconds. At this temperature, a glow was clearly visible from the tip.Thus, the current necessary to induce tip glow was established to be 4.6A. The source was then allowed to cool for 5 minutes.

Next, a negative bias was applied to the tip while monitoring electronemission current from the tip. The bias was made increasingly negativeuntil an electron emission current of 50 pA from the tip was observed.The tip bias at this current was −1.98 kV. With this bias still appliedto the tip, the heating current of 4.6 A was applied to the tip. Tipglow was again observed after about 20 seconds. Heating of the tipextended another 10 seconds after tip glow was observed. The biaspotential and heating current applied to the tip were then removed fromthe tip, and the tip was allowed to cool to liquid nitrogen temperature.

Once the tip had cooled, a positive bias of +5 kV relative to theextractor was applied to the tip. He gas was admitted to the FIM chamberin the vicinity of the tip, at a pressure of 1×10⁻⁵ Torr. FIM images ofthe tip apex were acquired as described in Example 1. The FIM image wasseen more clearly as the bias was increased. The image in FIG. 48 wasobserved at a tip bias of +13.92 kV. The image shows ridges of a pyramidand a bright central apex corresponding to an atomic trimer.

Some of the emitting atoms on the tip were loosely bound adatoms andwere removed with increased field strength via field evaporation of tipatoms. The tip bias was further increased, and first and second trimerswere removed by field evaporation to +21.6 kV. After reaching thispotential, the tip bias was reduced to +18.86 kV and the FIM image ofthe tip in FIG. 49 was recorded.

Based on the criteria identified in Example 1, the tip was identified asviable and removed from the FIM. About one month later, the tip wasmounted into a helium ion microscope configured as described inExample 1. The trimer was re-built and evaporated multiple times in aprocess as described in Example 1, except that no oxygen gas was used.Instead, the trimer rebuild process relied upon applying a specificnegative potential bias to the tip (to produce an electron emissioncurrent of 50 pA), while simultaneously heating the tip with a 4.6 Acurrent applied to the heater wire, resulting in visible glow of theheater wire for 20 seconds. The tip remained in the helium ionmicroscope and provided over four weeks of usage without the need tovent the system to service the tip. During this period, the tip wasrebuilt multiple times using the procedure involving a negative appliedpotential bias and heating, as discussed above. A SFIM image of are-built trimer of the tip is shown in FIG. 50.

An image of a semiconductor sample recorded using a He ion microscopewith this tip is shown in FIG. 51. The sample was included lines ofaluminum metal deposited on the surface of a silicon oxide substrate. Anunknown coating was deposited atop each of these materials.

Scan voltages of maximum amplitude 1 V were introduced on the scanningdeflectors to produce a 10 μm field of view on the sample. Thepotentials of the first and second lenses, the alignment deflectors, andthe astigmatism corrector were adjusted to control the portion of the Heion beam that passed through the aperture, and to control the quality ofthe beam focus at the sample position, as described in Example 1. Thesample was tilted and rotated during imaging to reveal the threedimensional nature and the details of the sidewalls.

The image shown in FIG. 51 was recorded by measuring secondary electronsfrom the surface of the sample. A MCP detector was positioned at adistance of 10 mm from the sample, and oriented parallel to the surfaceof the sample. The MCP grid and front surface were biased at +300 V,relative to the common external ground. The He ion beam current was 4 pAand the average ion energy was 21.5 keV. The total image acquisitiontime was 30 s.

An image of another semiconductor sample taken using this tip is shownin FIG. 52. The sample was a multilayer semiconductor device withsurface features formed of a metal. The image was recorded by measuringsecondary electrons that left the sample of the sample due to theinteraction of the sample with the incident He ions. Maximum scanvoltages of 150 volts were applied to the scanning deflectors to producea 1.35 mm field of view at the sample surface.

The sample was observed from a top down perspective, which shows manyfeatures on the surface of the sample. To record the image, a MCPdetector with grid and front surface biased at +300 V relative to thecommon external ground was positioned at a distance 10 mm from thesample, and oriented parallel to the surface of the sample. The He ionbeam current was 15 pA and the average ion energy was 21.5 keV. The ionbeam was raster-scanned with a dwell time of 10 μs per pixel.

3

The tip in this example was prepared and aligned in the helium ionmicroscope using a procedure as described in Example 2. Geometricalcharacterization of the tip was performed according to the procedure inExample 1. The tip was accepted for use based on the criteria in Example1.

By direct or extrapolated measurement, it was possible to acquire imagesof a sample at a known beam current and for a known acquisition time.The beam current was carefully monitored using a Faraday cup inconjunction with a pico-ammeter (Model 487, Keithley Instruments,Cleveland, Ohio). The He pressure in the tip region was also carefullymonitored using a Baynard Alpert-type ionization gauge (available fromVarian Vacuum Inc, Lexington, Mass.). In a regime in which the He ioncurrent was too low to be accurately measured (e.g., less than about 0.5pA), the ion current was determined by extrapolation based on themeasured He gas pressure. Typically, the He gas pressure and He ioncurrent are linearly proportional to one another, and the linearrelationship is consistent from one tip to another.

The sample was a gold grid sample with topographic features (part number02899G-AB, obtained from Structure Probe International, West Chester,Pa.). The sample was imaged by measuring secondary electron emissionfrom the sample surface in response to incident He ions. To recordimages, a 40 mm diameter annual, chevron-type MCP detector (obtainedfrom Burle Electro-Optics, Sturbridge, Mass.) was positioned at adistance 10 mm from the sample, and oriented parallel to the surface ofthe sample. The detector consumed a solid angle of about 1.8 steradiansand was symmetric with respect to the ion beam. The detector was mounteddirectly to the bottom of the second lens, as shown in FIG. 66. Thefront surface of the MCP was biased positively (+300 V) with respect tothe common external ground, and there was also a positively biased (withrespect to the common external ground) internal metal grid (+300 V).

The average ion energy was 20 keV. Images of the sample were measuredwith beam currents of 1 pA, 0.1 pA and 0.01 pA, respectively, and areshown in FIGS. 53, 54, and 55, respectively. The total image acquisitiontimes were 33 seconds, 33 seconds, and 67 seconds, respectively.

For the first two images (FIGS. 53 and 54), the image size was 1024×1024pixels. For the third image (FIG. 55), the image size was 512×512pixels. In each image, maximum scan voltages of about 2 V were appliedto the scanning deflectors to produce a 20 μm field of view at thesample surface.

To confirm that scattered helium ions and/or neutral atoms did notcontribute significantly to these recorded images, the grid and MCP biaspotentials were changed to −50 V, whereupon no signal was observed. Thenoise content of these images was recognized as being lower than thenoise content that would be attained with SEM images of the sample forthe same current, the same number of pixels, and the same totalacquisition time.

4

A tip was mounted in a support assembly and fabricated using methods asdescribed in Example 1, except that in the support assembly, the twoposts attached to the source base were pre-bent towards each other, asshown in FIG. 56. The bend permitted the heater wire to span asignificantly shorter length. The heater wire was as described inExample 1, a polycrystalline tungsten wire with a diameter of 180 μm.With the bent posts, a heater wire length of 5 mm was used. Theadvantage of a shorter heater wire length that the stiffness of a lengthof wire increases as the length of the wire decreases. The emitter wirewas affixed in the usual way as described in Example 1.

The increased stiffness of the shorter heater wire was observed byapplying the same force to a two different tips, one mounted in asupport assembly of the type described in Example 1, and the othermounted in the support assembly shown in FIG. 56. The deflections of thetwo tips in response to the applied force were compared. In comparisonto the Example 1-type support base, the bent post support assembly wasdeflected by an amount that was a factor of 6 smaller. Consequently thenatural vibration frequency of the bent post-type support assembly(approximately 4 kHz) was about 2.5 times higher than the naturalfrequency of the support assembly of Example 1. With a higher frequency,the support base and the tip moved in unison (e.g., with negligiblephase shift) when excited at vibrational frequencies substantially belowthe natural vibration frequency. When implemented in a He ionmicroscope, the relatively low vibration of the tip in the bent postsource assembly reduced the likelihood that ion microscope images wouldhave appreciable image artifacts, such as beam landing errors, due totip vibrations.

5

A tip was prepared according to the procedure described in Example 1,except that a different heater wire was used. The heater wire used inthis example had a diameter that was larger than the diameter of theheater wire in Example 1 by about 25%. The thicker heater wire was lesscompliant with respect to vibrational motion, because, in general, thestiffness of a wire increases with increasing diameter. In addition, thethicker heater wire was formed from a tungsten-rhenium alloy (74%Tungsten, 26% Rhenium). The alloy wire had a significantly higherelectrical resistivity than the tungsten heater wire of Example 1; theoverall heater wire resistance was measured to be approximately 0.5ohms. Suitable tungsten-rhenium alloy wires were obtained from OmegaEngineering (Stamford, Conn.).

The thicker heater wire increased the natural frequency of the supportassembly, including the tip, from about 1.5 kHz (Example 1) to about 2.2kHz (this example). When implemented in the He ion microscope, therelatively low vibration of the tip in the source assembly with thisheater wire assembly reduced the likelihood that ion microscope imageswould have appreciable image artifacts, such as beam landing errors, dueto tip vibrations.

6

A tip was formed by a process as described in Example 1, except that theheater wire was replaced by blocks of pyrolytic carbon (obtained fromMINTEQ International Pyrogenics Group, Easton, Pa.). The posts of thesource assembly were bent towards one another and were machined to haveparallel flat surfaces. To mount the emitter wire, the posts were priedapart and two blocks of pyrolytic carbon were inserted between theposts. The emitter wire was placed between the carbon blocks and thenthe posts were released. The compressive force applied to the carbonblocks by the posts held the blocks and the emitter wire in place on thesupport assembly, preventing relative motion of the emitter wire withrespect to the support base. A portion of the support assembly,including the bent posts, the two carbon blocks, and the emitter wire,is shown in FIG. 57.

The size of the pyrolytic carbon blocks was chosen so that the carbonblocks and the emitter wire were in compression. Without the carbonblocks in place, the space between the bent posts was 1.5 mm. The carbonblocks each had a length 700 μm along a direction between the two bentposts. The emitter wire had a diameter of 250 μm.

The pyrolytic carbon blocks were oriented with respect to the bent postsfor maximum electrical resistance and minimum thermal conductivity(e.g., with carbon planes in the pyrolytic carbon blocks orientedapproximately perpendicular to a line joining the posts). The electricalresistance of the support assembly was measured to be 4.94 ohms at 1500K, which is larger than the resistance of the support assembly ofExample 1 (0.56 ohms). The power required to heat the tip to 1500 K was6.4 W (compared to about 11 W required to heat the tip in Example 1 to1500 K). The tip was held relatively rigid with respect to the sourcebase, due to the absence of a heater wire. The natural vibrationfrequency of the support assembly was greater than 3 kHz.

When implemented in the helium ion microscope, the relatively lowvibration of the tip in this source assembly—held in position bycompressive force applied to pyrolytic carbon blocks on either side ofthe tip—reduced the likelihood that ion microscope images would haveappreciable image artifacts, such as beam landing errors, due to tipvibrations.

7

A tip was prepared following a procedure as described in Example 1, andcharacterization of geometrical tip properties was performed in asdescribed in Example 1. The tip was accepted for use based on thecriteria in Example 1.

The tip was sharpened in the FIM using the procedure described inExample 1. The tip was then installed and configured in the He ionmicroscope. The microscope system was configured as described in Example1, with changes to the configuration noted below.

The microscope system was configured to measure secondary electrons thatleft the sample due to the interaction of the sample with the incidentHe ions. A MCP detector (similarly configured to the detector describedin Example 3) was used to record sample images.

The sample was steel, and was spherical in shape and of uniformcomposition. The He ion beam current was 1.0 pA and the average ionenergy was 20 keV. The ion beam was raster-scanned with a dwell time of10 μs per pixel. The maximum potentials applied to the scanningdeflectors (about 100 V) yielded a field of view at the surface of thesample of about 1 mm.

An image of the sample is shown in FIG. 58. The image reflects ameasurement of the total secondary electron yield for the sample. Theimage reveals enhanced secondary electron yield at the right-hand edge.The enhanced yield resulted from the increased path length of the ionbeam near the surface of the sample, where secondary electrons canescape. The secondary electron yield was found to increase approximatelyin proportion to sec(α), where α represents the angle between theincident He ion beam and a normal to the surface of the sample.

Images of a second sample are shown in FIGS. 59A and 59B. The imagingconditions for the sample shown in FIG. 59A were as discussed above inconnection with the first sample in this example.

At energies of 20 keV, the He ion beam penetrated deeply into the sample(about 100 nm) before diverging significantly. As a result, the edges ofsample images showed a relatively narrower bright edge effect (e.g.,reduced edge blooming). For example, the image in FIG. 59A was recordedfrom the He ion microscope, while the image in FIG. 59B was recordedusing a standard SEM. In both images, the signal arises from ameasurement of secondary electrons only. In the SEM image shown in FIG.59B, the SEM was operated under imaging conditions which were 2 keVelectron beam energy and 30 pA beam current.

The bright edges were observed to be appreciably narrower in the He ionmicroscope images, which is believed to be a consequence of the smallerinteraction volume of He ions at the surface of the sample in comparisonto incident electrons. The He ion beam remains relatively collimated asit passes into the sample. In contrast, the SEM's electron beam yieldsan interaction volume which is considerably wider immediately adjacentto the surface of the sample. As a result, secondary electrons generatedby the incident electron beam arise from a surface region that extendsseveral nanometers from the nominal electron beam position on thesurface. Consequently, the SEM's bright edge effect was substantiallywider, as can be seen by visually comparing the images in FIGS. 59A and59B.

To numerically compare the bright edge effect in these two images, aline scan was performed across a common edge feature in each of theimages. The results are shown in FIGS. 67A and 67B, which correspond toFIGS. 59A and 59B, respectively. The line scan area was 1 pixel wide by50 pixels long. The intensity peak in the line scan—which corresponds tothe edge feature—has a full width at half-maximum (FWHM) that is 40%wider in the SEM image than in the corresponding He ion microscopeimage. As noted above, the reduced edge width observed in the He ionmicroscope image is a result of the smaller interaction volume of Heions at the surface of the sample, relative to electrons.

8

A tip was prepared following a procedure as described in Example 1, andcharacterization of geometrical tip properties was performed asdescribed in Example 1. The tip was accepted for use based on thecriteria in Example 1.

The tip was sharpened in the FIM using the procedure described inExample 1. The tip was then installed and configured in the He ionmicroscope. The microscope system was configured as described in Example1, with changes to the configuration noted below.

The microscope system was configured to measure secondary electrons thatleft the sample due to the interaction of the sample with the incidentHe ions. A MCP detector (as described in Example 3) was used to recordsample images.

A variety of samples were measured to quantitatively determine thesecondary electron yield for a number of materials. Each sampleconsisted of a flat piece of the material to be tested. Positioned abovethe sample, at a distance of 2 mm was a metal screen with a lowfill-factor (e.g., mostly open space). A pico-ammeter (KeithleyInstrument Corporation, Cleveland, Ohio) was used measured the samplecurrent in conjunction with a Faraday cup, which was integrated intoeach sample by machining a groove into the surface of each sample.

Each experiment began with a measurement of the He ion current bypositioning the He ion beam such that it was incident on the Faraday cupin each sample. Next, the He ion beam was rastered over the sample whilea variable bias, relative to the common external ground, was applied tothe screen, and the secondary electron current from the sample wasmeasured.

The He ion beam was intentionally defocused (to a spot size of 100 nm)to minimize any contamination or charging artifacts. The screen biaspotential was adjusted in increments from −30 V to +30 V, and thesecondary electron current was measured for each bias potential. Eachmeasurement was conducted with a He ion beam energy of 22.5 keV and abeam current of 13 pA. The graph in FIG. 60 shows the results for asilicon sample.

On the left of the graph, where the screen was biased negatively, all ofthe secondary electrons that left the sample due to the interaction ofthe sample with the incident He ions were returned to the siliconsample. The He ion beam current and the secondary electron current wereapproximately equal, so that negligible amounts of free secondary ionsand scattered helium ions were produced. On the right of the graph,where the screen was biased positively, all of the secondary electronsthat left the sample due to the interaction of the sample with theincident He ions were accelerated away from the sample. The measuredsample current was the sum of the He ion current and the secondaryelectron current. Based on these measurements, the secondary electronyield for a 22.5 keV helium beam incident (at a normal incidence) on aflat silicon sample is approximately (44-13)/13=2.4.

A similar measurement procedure was followed for a variety of materialsunder similar measurement conditions. The results are summarized in thetable below. Material Secondary Electron Yield Aluminum 4.31 Silicon2.38 Titanium 3.65 Iron 3.55 Nickel 4.14 Copper 3.23 Indium 4.69Tungsten 2.69 Rhenium 2.61 Platinum 7.85 Gold 4.17 Lead 4.57

These relatively large secondary electron yields, and the wide range ofvalues for different materials, account for the general observation thatHe ion microscope images based on detection of secondary electronsprovide a good way to distinguish different materials. As an example,FIG. 61A is a secondary electron image of an alignment cross on thesurface of a substrate, recorded using the helium ion microscope. Scanvoltages of maximum amplitude of about 1.5 V were introduced on thescanning deflectors to produce a 15 μm field of view on the sample. AMCP detector was positioned at a distance of 10 mm from the sample, andoriented parallel to the surface of the sample. The grid and front faceof the MCP were biased at +300 V, relative to the common externalground. The He ion beam current was 5 pA and the average ion energy was27 keV. The ion beam was raster-scanned with a dwell time of 150 μs perpixel.

FIG. 61B is a SEM secondary electron image taken of the same feature.The SEM was operated under experimentally determined optimum imagingconditions, which were 2 keV electron beam energy and 30 pA beamcurrent. Other beam currents, scan speeds, and beam energies were tried,but none of them offered a better contrast.

The He ion microscope image shows greater contrast between the differentmaterials that form the alignment cross because of the largerdifferences in secondary electron yield for an incident He ion beam,relative to an incident electron beam. The two materials in thealignment cross can readily be distinguished visually in the image ofFIG. 61A. However, as observed qualitatively in FIG. 61B, the twomaterials have similar secondary electron yields for the incidentelectron beam of the SEM.

9

A tip was prepared following a procedure as described in Example 1, andcharacterization of geometrical tip properties was performed asdescribed in Example 1. The tip was accepted for use based on thecriteria in Example 1.

The tip was sharpened in the FIM using the procedure described inExample 1. The tip was then installed and configured in the He ionmicroscope. The microscope system was configured as described in Example1, with changes to the configuration noted below.

The microscope system was configured to measure secondary electrons thatleft the sample due to the interaction of the sample with the incidentHe ions. A MCP detector (as described in Example 3) was used to recordsample images. The front end of the MCP was biased to +100 V, relativeto the common external ground, as was the grid in front of it. In thisconfiguration, the MCP was capable of collecting nearly all of thesecondary electrons that left the sample due to the interaction of thesample with the incident He ions, except for secondary electrons whichwere produced in a region of the sample which was biased positively.These electrons returned back to the sample due to the positive voltagebias instead of being fully liberated from the sample and detected bythe MCP.

Regions of the sample were positively biased due both to arrivingpositive charges from the incident He ion beam, and to departingnegative charges (secondary electrons). The magnitude of the inducedvoltage bias on the sample for a given He ion beam current was dependentupon the electrical capacitance and/or resistance of the exposed regionof the sample, relative to the surrounding portions of the sample. Thesedifferences lead to different secondary electron collection fordifferent regions of the sample, according to capacitive and/orresistive properties of the sample. The differences in detectedsecondary collection produces contrast in images of the sample recordedusing the He ion microscope. In this manner, electrical properties ofthe sample were determined based on secondary electron images.

In FIG. 62, a secondary electron image of a sample is shown. The samplefeatured a set of aluminum lines deposited on the surface of aninsulating substrate. Scan voltages of maximum amplitude 3 V wereintroduced on the scanning deflectors to produce a 30 μm field of viewon the sample. The He ion beam current was 5 pA and the average ionenergy was 26 keV. The ion beam was raster-scanned with a dwell time of100 μs per pixel.

The sample image shows a series of bright, periodic aluminum lines. Inthe spaces between these bright lines are a series of darker lines. Themiddle bright line in the image shows a distinct boundary, beyond whichthe line is dark. Based on the nature of the sample, the bright lineshave a low resistance path to ground, or perhaps a very high capacitancerelative to ground, and hence they were not substantially biased due tothe action of the He ion beam.

The dark lines were biased positively under the influence of the He ionbeam, and hence the secondary electrons produced there returned back tothe sample. To determine whether this effect was due to the capacitiveor resistive properties of the dark lines, the dark lines were observedover a period of time under the He ion beam. If the effect wascapacitive in nature, the lines became increasingly dark over time.

The transition from light to dark for the middle aluminum line mayindicate the presence of an electrical disconnect, for example, on theline. The lower, bright portion of the line may not be in fullelectrical contact with the upper, dark portion of the line.

FIG. 63 shows an image of another sample recorded using the measurementconfiguration described above. The sample includes lines and otherfeatures formed of copper on a silicon substrate. The smallest featuresare in the form of letters (“DRAIN”). The positive potential bias onthese features increased over the course of image acquisition, asevidenced by the observation that the top of each character appearsbright while the bottom of each character appears dark. The raster scanin this image proceeded from top to bottom. As a result, biasingmechanism on the surface features of the sample is primarily capacitive.

10

A tip was prepared following a procedure as described in Example 1, andcharacterization of geometrical tip properties was performed asdescribed in Example 1. The tip was accepted for use based on thecriteria in Example 1.

The tip was sharpened in the FIM using the procedure described inExample 1. The tip was then installed and configured in the He ionmicroscope. The microscope system was configured as described in Example1, with changes to the configuration noted below.

The microscope system was configured to measure secondary electrons thatleft the sample due to the interaction of the sample with the incidentHe ions. A MCP detector (as described in Example 3) was used to recordsample images. The front end of the MCP was biased to +300 V, relativeto the common external ground, as was the grid in front of it. In thisconfiguration, the measured signal arose almost entirely from secondaryelectrons. This was verified by biasing the MCP front end to −300 V,without changing the MCP gain, and observing that the measured signalwas diminished to nearly zero.

Scan voltages of maximum amplitude 3 V were introduced on the scanningdeflectors to produce a 30 μm field of view on the sample. The He ionbeam current was 10 pA and the average ion energy was 22 keV. The ionbeam was raster-scanned with a dwell time of 100 μs per pixel.

A sample that included three distinct layers was imaged. The top mostmetal layer consisted of patterned lines formed of copper. The nextlayer consisted of a dielectric material. The bottom layer consisted ofanother, differently patterned metal layer formed of copper. The imageof the sample is shown in FIG. 64. The image clearly shows the topmostmetal layer pattern in bright white, superimposed upon grey imagefeatures that correspond to the bottom (sub-surface) metal layer. Thesub-surface metal layer appears both dimmer and slightly blurred in theimage.

The measured signal was the result of secondary electrons generated atthe surface of the sample by both scattered He ions and neutral Heatoms. This assessment was verified by biasing the MCP and screennegative and noting that almost no signal was detected. Secondaryelectrons that left the sample due to the interaction of the sample withthe incident He ions produced the image of the surface metal layer inFIG. 64. The image of the sub-surface metal layer is produced He ionsthat have penetrated into the sample and become neutralized. The neutralHe atoms scatter from the sub-surface layer, and a fraction of themreturn to the surface where they produce secondary electrons upon theirexit. This accounts for the blurred and dimmed image of the sub-surfacefeatures.

11

A tip was prepared following a procedure as described in Example 1, andcharacterization of geometrical tip properties was performed asdescribed in Example 1. The tip was accepted for use based on thecriteria in Example 1.

The tip was sharpened in the FIM using the procedure described inExample 1. The tip was then installed and configured in the He ionmicroscope. The microscope system was configured as described in Example1, with changes to the configuration noted below.

The microscope system was configured to measure secondary electrons thatleft the sample due to the interaction of the sample with the incidentHe ions. A MCP detector (as described in Example 3) was used to recordsample images. The front end of the MCP was biased to +300 V, relativeto the common external ground, as was the grid in front of it. In thisconfiguration, the measured signal arose almost entirely from secondaryelectrons. This was verified by biasing the MCP front end to −300 V,without changing the MCP gain, and observing that the measured signalwas diminished to nearly zero.

Scan voltages of maximum amplitude 15 V were introduced on the scanningdeflectors to produce a 150 μm field of view on the sample. The He ionbeam current was 10 pA and the average ion energy was 21.5 keV. The ionbeam was raster-scanned with a dwell time of 100 μs per pixel.

The sample that was imaged consisted of a piece of a tungsten weld. Thetungsten had been heated to above its melting point and had subsequentlycooled, forming distinct crystallographic domains, with abruptboundaries between crystal grains. The sample was imaged by measuringsecondary electrons that left the sample due to the interaction of thesample with the incident He ions.

An image of the sample is shown in FIG. 65. The image shows distinctlybrighter and darker grains. Superimposed on this background are brightimage features which span several grains. The bright features correspondto surface topographic relief patterns, which enhance secondary electronproduction due to the topographic effects disclosed herein. Thecontrasting image intensities of the various crystal grains were due tothe relative orientations of the crystal domains with respect to theincident He ion beam. When the tungsten lattice in a particular grainwas oriented so that the He ion beam enters approximately parallel to alow index crystallographic direction, the scattering probability at thesurface was low, and so the ion beam penetrated deeply into the grain.As a result, the secondary electron yield at the surface of the materialwas relatively lower, and the grain appeared darker in the image.Conversely, when the tungsten lattice in a particular grain was orientedso that the He ion beam was incident upon a high index crystallographicdirection, the scattering probability at the surface of the grain washigh. As a result, the secondary electron yield at the surface of thematerial was relatively higher, and the grain appeared brighter in theimage.

12

A tip was prepared following a procedure as described in Example 1, andcharacterization of geometrical tip properties was performed asdescribed in Example 1. The tip was accepted for use based on thecriteria in Example 1.

The tip was sharpened in the FIM using the procedure described inExample 1. The tip was then installed and configured in the He ionmicroscope. The microscope system was configured as described in Example1, with changes to the configuration noted below.

The microscope system was configured to measure He ions and neutral Heatoms scattered from a sample in response to incident He ions. A MCPdetector (as described in Example 3) was used to record sample images.The front end of the MCP was biased to −100 V, relative to the commonexternal ground, as was the grid in front of it. In this configuration,secondary electrons do not reach the MCP due the negative appliedpotential bias. The signal measured by the MCP arises from scattered Heions and neutral He atoms that are incident on the front face of theMCP.

Scan voltages of maximum amplitude 15 V were introduced on the scanningdeflectors to produce a 150 μm field of view on the sample. The He ionbeam current was 10 pA and the average ion energy was 21.5 keV. The ionbeam was raster-scanned with a dwell time of 100 μs per pixel.

The imaged sample was the tungsten weld sample that was also examined inExample 11. As before, the tungsten weld included distinctcrystallographic domains, with abrupt boundaries between the grains.

The sample was imaged by detecting the abundance of He atoms and He ionsincident on the MCP. An image of the sample obtained using thismeasurement procedure is shown in FIG. 68. The image shows both brightand dark grains. For a particular crystalline grain, if the tungstenlattice in the grain was oriented so that the He ion beam was incidentalong a relatively low index crystallographic direction, there was a lowprobability of He scattering at the surface of the grain. As a result,ions penetrated relatively deeply into the grain before scatteringoccurred. As a result, the He ions (or He neutral atoms, produced whenHe ions combine with an electron in the sample) are less likely to leavethe sample and be detected by the MCP detector. Grains having theseproperties appeared dark in the recorded image.

Conversely, if the tungsten lattice in a particular grain was orientedso that the He ion beam was incident along a relatively high indexcrystallographic direction, there was a relatively high probability ofHe scattering at the surface of the grain. As a result, penetration ofthe He ions into the sample before scattering was, on average,relatively shallow. As a result, He ions and/or neutral He atoms wererelatively more likely to leave the surface of the sample and bedetected by the MCP detector. Grains with high-index crystalorientations with respect to the incident He ion beam therefore appearedbrighter in image shown in FIG. 68.

With reference to the image shown in FIG. 65, topographic information inthe image of FIG. 68 was significantly reduced because the image wasrecorded based on scattered He particles, rather than on secondaryelectrons. In particular, the series of bright lines that appeared onthe image in FIG. 65 were largely removed from the image in FIG. 68. Theabsence of topographic information can make the image in FIG. 68relatively easier to interpret, especially where the measuredintensities in FIG. 68 are used to quantitatively identify thecrystallographic properties (such as the relative orientation) ofcrystalline domains in the sample.

13

A tip was prepared following a procedure as described in Example 1, andcharacterization of geometrical tip properties was performed asdescribed in Example 1. The tip was accepted for use based on thecriteria in Example 1.

The tip was sharpened in the FIM using the procedure described inExample 1. The tip was then installed and configured in the He ionmicroscope. The microscope system was configured as described in Example1, with changes to the configuration noted below.

The microscope system was configured to measure He ions and neutral Heatoms scattered from a sample in response to incident He ions. Adetector—a miniature MCP—was mounted on the shaft of an electricalmotor. Copper tape was used to cover the front face of the MCP torestrict measurement of He ions and/or neutral atoms by the MCP. A smallcircular hole in the copper tape permitted scattered He ions and/orneutral atoms to reach the MCP only if the particles fell within anarrow angular range. In this example, measurement of He ions and/orneutral atoms was restricted to an angular range corresponding to asolid angle of 0.01 steradians. The copper tape and the front of the MCPwere biased to −100 V, relative to the common external ground, so thatsecondary electrons would not enter the MCP detector.

The detector was positioned at a distance of 30 mm from the sample. Themotor permitted rotation of the MCP detector with respect to the sampleto detect He ions and/or neutral atoms leaving the sample surface at arange of different angles. Typically, for example, the motor permittedrotation of the MCP through approximately 180°.

The sample was a copper ball of diameter of approximately 1 mm. Themotor was positioned relative to the sample such that the sample waslocated along the axis of the motor shaft. The copper ball sample, whenexposed to the He ion beam, provided scattered He ions and neutral Heatoms at a wide range of angles, due to the shape of the sample surface.That is, by scanning the incident He ion beam across the surface of thesample, a variety of different angles of incidence (e.g., the anglebetween the He ion beam and a normal to the sample surface) can berealized. For example at the center of the copper ball, the angle ofincidence of the He ion beam is 0°. At the edge of the ball (as observedfrom the perspective of the He ion beam), the angle of incidence isapproximately 90°. At a position half-way between the center and theedge of the copper ball, the angle of incidence is approximately 30°from simple trigonometry.

The sample was positioned under the He ion beam, and the detector waspositioned with respect to the sample as described above. The He ionbeam current was 15 pA, and the average ion energy in the He ion beamwas 25 keV. A maximum voltage of 100 V was applied to the scanningdeflectors to achieve a 1 mm field of view at the surface of the sample.The distance from the second lens of the microscope system to the sample(e.g., the working distance) was 75 mm. This provided enough open spaceto allow the MCP detector to rotate with respect to the sample.

The measurements were performed by recording images of the copper ballwhile the detector was swept through a 180° range of angles in ahemispherical arc with respect to the sample. The He ion beameffectively partitioned the surface of the sample into two sides and,due to the convex surface of the copper ball, scattered He ions andneutral He particles could only be detected from the side on which thedetector was positioned. As a result, in FIG. 69A, the intensity profileof the image of the sample appears crescent-shaped, with the brightregion on the left corresponding to the position of the detector. Theright side of the sample was relatively dark, since scattered He ionsand neutral He particles left the surface of the sample in directionssuch that they could not be measured by the detector.

Successive images of the sample were recorded by incrementing thedetector angle between each image. A total of 20 images of the samplewere acquired, spanning the scanning range of the detector. Certainimages did not provide useful information because the detector waspositioned such that it obstructed the incident He ion beam, preventingHe ions from being incident on the sample surface. The images shown inFIGS. 69B and 69C correspond to images of the sample recorded with thedetector positioned nearly directly above the sample and on the rightside of the sample, respectively. In FIG. 69C, a crescent-shapedintensity profile is observed that is analogous to the profile observedin FIG. 69A.

Based on qualitative inspection of the recorded images, it was evidentthat topographic information about the sample could be determined fromimages measured with the detector in off-axis positions (e.g., FIGS. 69Aand 69C). The information acquired from these measurements could becombined with secondary electron measurements of the sample, forexample, to ascertain whether image contrast observed in the secondaryelectron images was due to the surface topography of the sample, or dueto another contrast mechanism such as sample charging or materialcomposition. With the detector in a known position, it was possible,based on the recorded images, to distinguish a bump on the surface ofthe sample from a depression. The small detector acceptance angle andthe known position of the detector for each recorded image could also beused to determine quantitative surface relief (e.g., height) informationfor the sample by measuring the shadow lengths of surface features inthe image and making use of the known angle of the incident He ion beamwith respect to the surface features.

Images of the sample also revealed that, depending upon the orientationof the detector with respect to the sample, certain edges of the sampleexhibited a bright edge effect, while other edges exhibited a dark edgeeffect (see FIG. 69A, for example). This information was used in thedesign of a detector that was configured to reduce the measurement oftopographic information from a sample. The detector design balanced thedetection angles to provide a nearly uniform edge effect. As a result,images of a sample such as a copper ball would appear uniformly bright,with variations in intensity arising from material differences in thesample.

The image data recorded from the sample was analyzed to determine howthe intensity of selected regions of the sample surface changed as thedetector was scanned. Variations in intensity were due to the angulardistribution of He ions and He neutral atoms that left the samplesurface, and this analysis provided information about the distributionof angles, which are sometimes referred to as emission lobes.

FIG. 70A shows an image of the sample recorded with the detector nearlyon-axis with the incident He ion beam; that is, the detector measuredscattered He ions and neutral He atoms at an angle of approximately 0°.A region of the sample surface, denoted by the rectangular box, wasisolated in a series of images and subjected to further analysis. In thediagram shown in FIG. 70B, the thick horizontal line schematicallyrepresents the surface of the sample, and the thin vertical representsthe incident He ion beam. The dots represent the average measuredintensity of scattered He ions and neutral He atoms at various detectorpositions. The dots are plotted on a polar scale, where the origin ofthe polar plot is the point of incidence of the He ion beam on thesurface of the sample. The angular position of a given dot correspondsto the angular position of the detector, and the radial distance fromthe origin to each dot represents the average measured intensity at thatparticular angular detector position. Individual images of the sample,each corresponding to a different detector position, were analyzed toprovide the angular intensity data shown in FIG. 70B. Each dotcorresponds to an image recorded at a different detector position.

The polar array of dots forms an emission lobe diagram. The diagram isapproximately circular in shape (except for a few missing points wherethe He ion beam was obstructed by the detector), and corresponds to acosine distribution about the origin.

In FIG. 71A, an image of the sample is shown with a superimposedrectangular box denoting a different region of the sample surface thatwas analyzed using multiple sample images to determine the angularintensity distribution of scattered He ions and neutral atoms from thesample. In this case, the scattering or emission angle was about 40°with respect to the incident He ion beam.

The polar plot of angular emission intensity shown in FIG. 71B wasconstructed in the manner described in connection with FIG. 70B above.The shape of the lobes at this angle indicated that scattering/emissionis preferentially directed away from the incident He ion beam.

This analysis was repeated on a variety of different regions of thesample surface (corresponding to a variety of different angles) to buildup a relatively complete picture of the distribution of scattered Heions and neutral He atoms as a function of angle for the copper ballsample.

14

A tip was prepared following a procedure as described in Example 1, andcharacterization of geometrical tip properties was performed asdescribed in Example 1. The tip was accepted for use based on thecriteria in Example 1.

The tip was sharpened in the FIM using the procedure described inExample 1. The tip was then installed and configured in the He ionmicroscope. The microscope system was configured as described in Example1, with changes to the configuration noted below.

The microscope system was configured to measure He ions and neutral Heatoms scattered from a sample in response to incident He ions. A MCPdetector (as described in Example 3) was used to record sample images.The front end of the MCP was biased to −300 V, relative to the commonexternal ground, as was the grid in front of it. In this configuration,secondary electrons do not reach the MCP due the negative appliedpotential bias. The signal measured by the MCP arises from scattered Heions and neutral He atoms that are incident on the front face of theMCP. From the sample's perspective, the MCP detected He ions and Heatoms from within a solid angle of approximately 1.8 steradians. Thesolid angle was azimuthally symmetric with respect to the incident beamas shown in FIG. 66.

From Example 13, the bright and dark edge effects observed for thecopper ball sample provided information regarding the design andconfiguration of a detector which, when used to image a sample bymeasuring scattered He ions and/or neutral He atoms, reduced the amountof topographic information in the measured signals, and more accuratelyreflected differences in material composition rather than differences inlocal surface topography of the sample. For the MCP detector shown inFIG. 66, a reduction in topographic information in images formed basedon measurements of scattered He ions and neutral He atoms was observedif the MCP was positioned at a working distance of approximately 25 mmfrom the sample.

Samples that included different materials could then be imaged and thematerials reliably distinguished visually from one another. A samplethat included four different materials—a nickel base layer, a carboncoating, a copper grid, and a gold wire—was imaged using the He ionmicroscope. The He ion beam current was 1.1 pA and the average He ionenergy was 18 keV. Maximum voltages of 4 V were applied to the scanningdeflectors to realized a field of view at the sample surface of 40 μm.The total image acquisition time was 90 s.

The resulting image is shown in FIG. 72. Different intensities wereobserved for each of the four different materials in the sample. This isa consequence of the fact that the scattering probability a He ionsincident upon a particular material depends upon the atomic number ofthe material. In FIG. 72, even materials with similar atomic numbers canbe distinguished. For example, copper (atomic number 29) isdistinguishable visually from nickel (atomic number 28).

FIG. 73 shows an image of a sample that includes a copper layerunderlying a silicon wafer, with an oxide layer overlying the wafer. Theimage was measured using a He ion microscope system configured fordetection of scattered He ions and neutral He atoms as described earlierin this example. The sample includes surface structural features thatwere produced by directing a laser to be incident on the sample surface.The laser caused an explosive eruption of the underlying copper layer.Visual inspection of the image reveals image contrast (e.g., imageintensity variations) that result from the different materials presentin the sample. From images such as the image in FIG. 73, thedistribution of different materials in a sample can be determined.

15

A tip was prepared following a procedure as described in Example 1, andcharacterization of geometrical tip properties was performed asdescribed in Example 1. The tip was accepted for use based on thecriteria in Example 1.

The tip was sharpened in the FIM using the procedure described inExample 1. The tip was then installed and configured in the He ionmicroscope. The microscope system was configured as described in Example1, with changes to the configuration noted below.

The microscope system was configured to measure photons emitted from asample in response to the incident He ion beam. An image of the samplewas constructed from the signal generated by a photomultiplier tube(model R6095, Hamamatsu Photonics K.K., Toyooka, Japan). Thephotomultiplier tube had an end-on window, a relatively high quantumefficiency, and a broad spectral response from 200 nm to 700 nm. Thetube was operated with a signal gain that could be increased up to 1200V, or to the point where the output signal reached the signal chain'swhite noise level without excessive saturation. The photomultiplier tubewas positioned at a distance of 15 mm from the sample and was orientedto face the sample. In this configuration, the tube subtended a solidangle of about 2 steradians.

A sample of sodium chloride (NaCl) was imaged using the photomultipliertube detector. For these measurements, the He ion beam current was 10 pAand the average He ion energy was 25 keV. The sample was raster-scannedwith a dwell time per pixel of 500 μs. A maximum voltage of 150 V wasapplied to the scanning deflectors to yield a field of view at thesample surface of 1.35 mm.

An image of the sample is shown in FIG. 74. Image contrast (e.g.,variations in image intensity) are apparent among different NaClcrystals. Photons can be produced in the sample via two differentmechanisms. First, photons can be produced via processes that areanalogous to the cathodoluminescence that is observed in SEM images. Inthis mechanism, atoms of the sample are excited to higher-lying energystates. Photons are emitted during the subsequent de-excitation process.When the He ions from the incident beam return to lower-lying energystates, photons are emitted.

Other samples which have been exposed to the He ion beam and from whichemitted photons have been detected include plastics, scintillators, andorganic materials.

16

A tip was prepared following a procedure as described in Example 1, andcharacterization of geometrical tip properties was performed asdescribed in Example 1. The tip was accepted for use based on thecriteria in Example 1.

The tip was sharpened in the FIM using the procedure described inExample 1. The tip was then installed and configured in the He ionmicroscope. The microscope system was configured as described in Example1, with changes to the configuration noted below.

The tip was biased at +19 kV, relative to the extractor, and He gas wasintroduced in the vicinity of the tip at a pressure of 2×10⁻⁵ Torr. AFaraday cup was placed beyond the second lens, and the first lens andalignment deflectors were used to focus the beam so that substantiallyall of the He ions originating from one of the tip trimer atoms passedthrough the aperture (diameter 600 μm, positioned 370 mm from the tip),and substantially all of the He ions originating from the other twotrimer atoms were blocked by the aperture. After passing through theaperture, the He ion beam was focused by the first lens into the Faradaycup. In this configuration, the astigmatism corrector, the scanningdeflectors, and the second lens were off.

The total He ion current originating from the tip atom was measured tobe 300 pA using a pico-ammeter (model 487, Keithley Instruments,Cleveland, Ohio) together with the Faraday cup. The Faraday cup was acylindrical metal cup with a depth-to-diameter ratio of about 6 to 1.

Thereafter, the first lens was turned off. Each of the He ions generatedat the tip continued to travel in a straight line, diverging from thetip. The aperture intercepted most of the He ion beam and allowed only asmall central portion of it to pass further down the remainder of theion column. The portion of the He ion beam that passed through theaperture was detected with the Faraday cup, yielding a measured He ioncurrent of 5 pA passing through the aperture. The angular intensity ofthe He ion beam was then calculated as the He ion beam current passingthrough the aperture (5 pA) divided by the solid angle of the aperturefrom the perspective of the tip. The half-angle of the cone formed bythe apex of the tip and the aperture was calculated as tan⁻¹(0.300/370)=0.046°=8.1×10⁻⁴ radians. The corresponding solid angle wascalculated as 2.1×10⁻⁶ steradians (sr). Based upon the solid angle, theangular intensity of the He ion beam was determined to be 2.42 μA/sr.

The brightness of the He ion source was determined from the He ion beamangular intensity and the virtual source size. The virtual source sizewas estimated by examining a FIM image of the tip recorded duringsharpening of the tip. From this image, it was evident that individualionization discs corresponding to the tip trimer atoms were notoverlapping. Further, it was known from the crystallography of tungstenthat the trimer atoms were separated by approximately 5 Angstroms.Therefore, the actual ionization disks were estimated to have a diameterof about 3 Angstroms.

The virtual source size is generally smaller than the actual ionizationarea. The virtual source size was determined using the general procedurediscussed previously: by back-projecting asymptotic trajectories of 100He ions once the ions were beyond the electric field region (e.g., theregion in the vicinity of the tip and the extractor) of the ion source.The back-projected trajectories moved closer to one another until theypassed through a region of space in which they were most closely spacedwith respect to one another, and then they diverged again. The circulardiameter of the closest spacing of the back-projected trajectories wasdefined to be the virtual source size.

As an upper bound, we used a value of 3 Angstroms for the diameter ofthe virtual source. Where the microscope is configured to permit only aportion of the He ion beam originating from a single tip atom to passthrough the aperture, the virtual source size can be considerablysmaller. The brightness was calculated as the angular intensity dividedby the area A of the virtual source size, A=π(D/2)². The brightness ofthe ion source was 3.4×10⁹ A/cm²sr.

The reduced brightness was calculated as the brightness divided by thevoltage used to extract the beam (e.g., the voltage bias applied to thetip). The tip to extractor voltage was 19 kV, and the reduced brightnesswas 1.8×10⁹ A/m²srV.

The etendue is a measure of the product of the He ion beam's virtualsource size and its angular divergence (as a solid angle). Using thebrightness determined above, the etendue was determined to be 1.5×10⁻²¹cm²sr.

The reduced etendue is the etendue multiplied by the He ion beamvoltage. The reduced etendue, based on the etendue calculated above, wasdetermined (using the tip bias voltage of +19 kV) to be 2.8×10⁻¹⁷cm²srV.

17

A tip was prepared following a procedure as described in Example 1, andcharacterization of geometrical tip properties was performed asdescribed in Example 1. The tip was accepted for use based on thecriteria in Example 1.

The tip was sharpened in the FIM using the procedure described inExample 1. The tip was then installed and configured in the He ionmicroscope. The microscope system was configured as described in Example1, with changes to the configuration noted below.

The microscope system was configured to measure secondary electronsusing an ET detector. The detector was positioned at a distance of 10 mmvertically (parallel to the He ion beam) from the sample, displaced 25mm laterally from the sample, and inclined towards the sample. The ETscreen was biased at a potential of +300 V, relative to the commonexternal ground.

The He ion beam current was 1 pA, and the average ion energy in the beamwas 22 keV. The He ion beam was raster-scanned across the surface of thesample with a dwell time per pixel of 100 μs. A maximum voltage of 100mV was applied to the scanning deflectors to yield a field of view of1000 nm on the surface of the sample.

The sample included gold islands formed on the surface of a carbonsubstrate, and was obtained from Structure Probe Inc. (West Chester,Pa.). An image of the sample recorded using the above measurementconfiguration is shown in FIG. 75. A region of the sample image, denotedby the rectangle superimposed on the image in FIG. 75, was selected toexamine the quality of edge contrast observed with the He ionmicroscope. The region designated by a rectangle includes anearly-vertical gold edge. The region includes 20 rows, each with 57pixels. An expanded view of the selected region is shown in FIG. 76.

Each row of the selected image region was individually analyzed asfollows. First, to reduce noise, each row was smoothed with a Gaussiankernel of bandwidth 3 pixels using the MathCAD ksmooth function (PTCInc., Needham, Mass.). FIG. 77 shows a graph on which pixel intensityvalues for one particular line (line #14) before smoothing (dots) andafter smoothing (curve) are plotted. The vertical axis corresponds tothe image intensity, ranging from 0 (black) to 255 (white). Thehorizontal axis corresponds to the pixel number, ranging from 0 (leftedge) to 57 (right edge).

For each intensity line scan in the selected region of the image, thecenter of the left to right light-to-dark transition was determined bylocating the minimum value of the first derivative of the intensity linescan. For edges with a left to right dark-to-light transition, thecenter of the transition would have been found by determining thelocation of the maximum value of the first derivative of the intensityline scan.

Each line was then trimmed to contain just 21 pixels. The trimmingoperation such that the transition point, the 10 pixels preceding thetransition point, and the 10 pixels following the transition point wereretained in each line. Intensity values for the first five pixels ineach trimmed line were averaged together and the average was identifiedas the 100% value. Intensity values for the final five pixels in eachtrimmed line were averaged together and the average was identified asthe 0% value. The smoothed data from each line scan was then rescaled interms of the 100% and 0% values. The rescaled data from FIG. 77 is shownin FIG. 78.

With reference to FIG. 78, the 75% and 25% values were determined withreference to the 0% and 100% values. The spot size of the He ion beamwas subsequently determined as the separation along the horizontal axisbetween the 25% and 75% values. Based upon the data in FIG. 78, the spotsize was determined to be 3.0 pixels. The pixel size was converted tonanometers using the known field of view in the measurementconfiguration and the number of pixels in the image. For thismeasurement, the field of view was 641 nm, and there were 656 pixelsspanning the field of view. The spot size of the He ion beam wastherefore determined to be 2.93 nm. This was repeated for each of the 20lines in the selected region of the image, and the results were averagedto yield a mean He ion beam spot size of 2.44 nm.

18

A tip was prepared following a procedure as described in Example 1, andcharacterization of geometrical tip properties was performed asdescribed in Example 1. The tip was accepted for use based on thecriteria in Example 1.

The tip was sharpened in the FIM using the procedure described inExample 1. The tip was then installed and configured in the He ionmicroscope. The microscope system was configured as described in Example1, with changes to the configuration noted below.

The microscope system was configured to measure scattered He ions andneutral He atoms leaving a sample surface in response to incident Heions. A MCP detector as described in Example 3 was positioned 10 mm fromthe sample. A potential bias of 0 V relative to the external ground wasapplied to the MCP grid and front face.

The He ion beam current was 1 pA and the average He ion beam energy was26 keV. The He ion beam was raster-scanned over the surface of thesample with a dwell time per pixel of 100 μs. A maximum potential of1.30 V was applied to the scanning deflectors to yield a field of viewat the surface of the sample of 13 μm.

The sample, which included a silicon wafer substrate with surfacefeatures formed of polysilicon, was known as the Metrocal and wasobtained from Metroboost (Santa Clara, Calif.). The sample was orientedso that the He ion beam was incident at a normal angle to the samplesurface. The sample was biased to +19.4 kV, relative to the commonexternal ground, so He ions in the incident ion beam arrived at thesample with a landing energy of 6.6 keV. The large electric fieldbetween the sample and the MCP detector prevented secondary electronsfrom reaching the detector. Substantially all of the secondary electronsthat left the sample returned to the sample surface under the influenceof the electric field. As a result, the MCP detector measured scatteredHe ions and neutral atoms. Neutral He atoms measured by the detector hada maximum energy of 6.6 keV, while He ions measured by the detector wereaccelerated up to a maximum energy of 26 keV by the time they reachedthe MCP.

FIG. 79 shows an image of the sample recorded using the measurementconfiguration described above. Various features on the surface of thesample have measured intensities which are relatively uniform, anddifferent from the intensity of the substrate. Visual inspection of theedges of the surface features reveals that there are no apparent brightedge effects (e.g., edge blooming) which can lead to saturation of thesignal chain, and can make the precise location of the edge difficult tofind. In addition, there is no visual evidence of charging artifacts onthe sample surface; such artifacts, if present, would manifest asvoltage contrast in the image.

A horizontal line scan through one of the sample's surface features isshown in FIG. 80. The horizontal axis of the line scan shows the pixelnumber, and the vertical axis indicates the measured image intensity atparticular pixels. For purposes of comparison, the same sample wasimaged in a Schottky Field Emission SEM (AMRAY model 1860) with a beamenergy of 3 keV and a beam current of 30 pA, at a magnification of30,000× (corresponding to a field of view of about 13 um). The resultingimage is shown in FIG. 81, and a horizontal line scan through the samefeature that was scanned in FIG. 80 is shown in FIG. 82.

The line scan in FIG. 82 showed significant bright edge effects, and thesignal chain at the edges of the imaged surface feature was nearlysaturated. In the body of the surface feature, the SEM line scan doesnot show a relatively uniform steady state intensity level. Instead, theintensity level in the body of the feature is either decreasing orincreasing everywhere but in a small region at the center of thefeature. Finally, the asymmetry of the SEM line scan indicates thattime-dependent charging of the surface feature was occurring during SEMexposure. In comparison, the line scan image of the feature recorded bydetecting scattered He ions and neutral He atoms shows considerablyreduced edge effects, and no apparent charging artifacts.

Multiple measurements of a particular feature on the surface of thesample could also have been performed. If multiple measurements of afeature were made, it would have been possible to ascertain statisticaldata about the dimensions of the measured feature. For example, the meanfeature width, the standard deviation of the feature width, and/or themean and standard deviation of the location of the first edge and/or thesecond edge of the feature could have been measured. Fourier methodscould also have been used to analyze the positions of the edges of oneor more features to determine the spectrum of spatial wavelengthscorresponding to the edge shapes.

19 Measurement of Topographic and Crystalline Information from a Sample

To measure topographic and crystalline information from a sample, thesample is fixed in position on a sample mount in a gas field ionmicroscope as described herein. The gas field ion microscope isconfigured to expose a 100 μm² FOV on the surface of the sample to a Heion beam having a beam current of 1 pA, an average ion energy of 20 keV,and a beam spot size on the surface of the sample of 0.1% of the FOV.

To measure crystalline information from the sample, the He ion beam israster-scanned in discrete steps over the FOV region of the samplesurface. A two-dimensional detector is used to capture an image ofscattered He ions from the surface of the sample at each step. Eachtwo-dimensional image corresponds to a Kikuchi pattern at a particularposition on the surface of the sample. Based on the Kikuchi pattern, thesample's crystal structure, lattice spacing, and crystal orientation atthat position can be determined. By measuring Kikuchi patterns atdiscrete steps throughout the FOV, a complete map of the sample'ssurface crystal structure is obtained.

To measure topographic information from the sample, a detector isconfigured to measure a total intensity of secondary electrons from thesample produced in response to the incident He ion beam. The He ion beamis raster-scanned in discrete steps over the entire FOV region of thesample surface, and the total intensity of secondary electrons ismeasured as a function of the position of the He ion beam on the samplesurface. The measured crystalline information is then used to removecontributions to the secondary electron intensity measurements thatarise from crystal structure variations in the sample. The correctedtotal secondary electron intensity values are used to construct agrayscale image of the sample, where the gray level at a particularimage pixel is determined by the corrected intensities of secondaryelectrons at a corresponding He ion beam position on the sample.Topographic information is provided by the image, which shows thesurface relief pattern of the sample in the FOV.

20 Measurement of Topographic and Crystalline Information from a Sample

To measure topographic and crystalline information from a sample, thesample is fixed in position on a sample mount in a gas field ionmicroscope as described herein. The gas field ion microscope isconfigured as described in Example 19.

To measure crystalline information from the sample, the He ion beam israster-scanned in discrete steps over the FOV region of the samplesurface. A detector is used to measured a total abundance of scatteredHe ions as a function of the position of the He ion beam on the samplesurface. The measured total abundance values are used to construct agrayscale image of the sample, where the gray level at a particularimage pixel is determined by the total measured abundance of He ions ata corresponding He ion beam position on the sample. Differently-orientedcrystal grains at the surface of the sample have different yields ofscattered He ions, and the image shows the differently-oriented crystalgrains as variable gray levels. Using the information in the image,crystal grains and grain boundaries can be identified at the samplesurface.

To measure topographic information from the sample, the total secondaryelectron intensity is measured as described in Example 19. The measuredcrystalline information is then used to remove contributions to thesecondary electron intensity measurements that arise from crystalstructure variations in the sample. The corrected total secondaryelectron intensity values are used to construct a grayscale image of thesample, where the gray level at a particular image pixel is determinedby the corrected intensities of secondary electrons at a correspondingHe ion beam position on the sample. Topographic information is providedby the image, which shows the surface relief pattern of the sample inthe FOV.

21 Measurement of Topographic and Crystalline Information from a Sample

To measure topographic and crystalline information from a sample, thesample is fixed in position on a sample mount in a gas field ionmicroscope as described herein. The gas field ion microscope isconfigured as described in Example 19.

To measure crystalline information from the sample, the He ion beam israster-scanned in discrete steps over the FOV region of the samplesurface. A detector is used to measured a total abundance of scatteredHe ions as a function of the position of the He ion beam on the samplesurface. The measured total abundance values are used to construct agrayscale image of the sample, where the gray level at a particularimage pixel is determined by the total measured abundance of He ions ata corresponding He ion beam position on the sample. Differently-orientedcrystal grains at the surface of the sample have different yields ofscattered He ions, and the image shows the differently-oriented crystalgrains as variable gray levels. Using the information in the image,crystal grains and grain boundaries can be identified at the samplesurface. Once the grain boundaries on the surface of the sample havebeen identified, the He ion beam is scanned from one grain to another onthe surface of the sample. At each position of the He ion beam, atwo-dimensional detector is used to capture an image of scattered heions from the surface of the sample. Each two-dimensional imagecorresponds to a Kikuchi pattern for a particular crystal grain at thesurface of the sample. Based on the Kikuchi pattern, the grain's crystalstructure, lattice spacing, and crystal orientation can be determined.By measuring a single Kikuchi pattern for each grain rather than at eachpixel throughout the FOV, a complete map of the sample's surface crystalstructure is obtained in a shorter time.

To measure topographic information from the sample, the total secondaryelectron intensity is measured as described in Example 19. The measuredcrystalline information is then used to remove contributions to thesecondary electron intensity measurements that arise from crystalstructure variations in the sample. The corrected total secondaryelectron intensity values are used to construct a grayscale image of thesample, where the gray level at a particular image pixel is determinedby the corrected intensities of secondary electrons at a correspondingHe ion beam position on the sample. Topographic information is providedby the image, which shows the surface relief pattern of the sample inthe FOV.

22 Measurement of Topographic and Crystalline Information from a Sample

To measure topographic and crystalline information from a sample, thesample is fixed in position on a sample mount in a gas field ionmicroscope as described herein. The gas field ion microscope isconfigured as described in Example 19.

Crystalline information from the sample is measured as described inExample 19.

To measure topographic information from the sample, a detector isconfigured to measure a total intensity of secondary electrons from thesample produced in response to the incident He ion beam. The sample istilted with respect to the He ion beam, so that the He ion beam isincident at a non-normal angle to the surface of the sample. The He ionbeam is raster-scanned in discrete steps over the entire FOV region ofthe sample surface, and the total intensity of secondary electrons ismeasured as a function of the position of the He ion beam on the samplesurface. The measured crystalline information is then used to removecontributions to the secondary electron intensity measurements thatarise from crystal structure variations in the sample. The correctedtotal intensity values are used to construct a grayscale image of thesample, where the gray level at a particular image pixel is determinedby the corrected total intensities of secondary electrons at acorresponding He ion beam position on the sample. Topographicinformation is provided by the image, which shows the surface reliefpattern of the sample in the FOV. Tilting the sample with respect to theHe ion beam can reveal topographic information that would otherwiseremain hidden if the He ion beam was incident on the sample surface onlyat normal angles.

Optionally, the sample tilt can then be adjusted so that the He ion beamis incident at a different non-normal angle to the surface of thesample, and the He ion beam is raster-scanned is discrete steps over theentire FOV region of the sample surface. The total intensity ofsecondary electrons is measured as a function of the position of the Heion beam on the sample surface, and the measured crystalline informationis used to remove contributions to the secondary electron intensitymeasurements that arise from crystal structure variations in the sample.The corrected total secondary electron intensity values are used toconstruct a second grayscale image of the sample corresponding to thesecond non-normal incidence angle of the He ion beam, where the graylevel at a particular image pixel is determined by the corrected totalintensities of secondary electrons at a corresponding He ion beamposition on the sample. The information from the two images measured atdifferent He ion beam angles of incidence can then be combined and usedto determine quantitative three-dimensional topographic informationabout the surface of the sample.

23 Measurement of Topographic and Crystalline Information from a Sample

To measure topographic and crystalline information from a sample, thesample is fixed in position on a sample mount in a gas field ionmicroscope as described herein. The gas field ion microscope isconfigured as described in Example 19.

Crystalline information from the sample is measured as described inExample 20.

To measure topographic information from the sample, the total intensityof secondary electrons from the sample is measured as described inExample 22. The measured crystalline information is used to removecontributions to the secondary electron intensity measurements, at eachion beam angle of incidence, that arise from crystal structurevariations in the sample. The corrected total secondary electronintensity values are used to construct grayscale images of the sample asdescribed in Example 22. The information from the two images measured atdifferent He ion beam angles of incidence can then be combined and usedto determine quantitative three-dimensional topographic informationabout the surface of the sample.

24 Measurement of Topographic and Crystalline Information from a Sample

To measure topographic and crystalline information from a sample, thesample is fixed in position on a sample mount in a gas field ionmicroscope as described herein. The gas field ion microscope isconfigured as described in Example 192.

Crystalline information from the sample is measured as described inExample 21.

To measure topographic information from the sample, the total intensityof secondary electrons from the sample is measured as described inExample 22. The measured crystalline information is used to removecontributions to the secondary electron intensity measurements, at eachion beam angle of incidence, that arise from crystal structurevariations in the sample. The corrected total secondary electronintensity values are used to construct grayscale images of the sample asdescribed in Example 22. The information from the two images measured atdifferent He ion beam angles of incidence can then be combined and usedto determine quantitative three-dimensional topographic informationabout the surface of the sample.

25 Measurement of Topographic and Crystalline Information from a Sample

To measure topographic and crystalline information from a sample, thesample is fixed in position on a sample mount in a gas field ionmicroscope as described herein. The gas field ion microscope isconfigured as described in Example 19.

Crystalline information from the sample is measured as described inExample 19.

To measure topographic information from the sample, two or moredetectors, each oriented at a different angle and position with respectto the sample, are configured to measure a total intensity of secondaryelectrons from the sample produced in response to the incident He ionbeam. The He ion beam is raster-scanned in discrete steps over theentire FOV region of the sample surface, and the total intensity ofsecondary electrons is measured by each detector as a function of theposition of the He ion beam on the sample surface. The measuredcrystalline information is used to remove contributions to the secondaryelectron intensity measurements at each detector that arise from crystalstructure variations in the sample. The corrected total intensity valuesare used to construct a series of grayscale images of the sample, eachimage corresponding to one of the detectors, where the gray level at aparticular pixel in a particular image is determined by the correctedtotal intensity of secondary electrons at a corresponding He ion beamposition on the sample. Information from the images measured by themultiple detectors can then be combined and used to determinequantitative three-dimensional topographic information about the surfaceof the sample.

26 Measurement of Topographic and Crystalline Information from a Sample

To measure topographic and crystalline information from a sample, thesample is fixed in position on a sample mount in a gas field ionmicroscope as described herein. The gas field ion microscope isconfigured as described in Example 19.

Crystalline information from the sample is measured as described inExample 20.

To measure topographic information from the sample, the total intensityof secondary electrons from the sample is measured as described inExample 25. The measured crystalline information is used to removecontributions to the secondary electron intensity measurements, at eachdetector, that arise from crystal structure variations in the sample.The corrected total secondary electron intensity values are used toconstruct grayscale images of the sample as described in Example 25.Information from the images measured by the multiple detectors can thenbe combined and used to determine quantitative three-dimensionaltopographic information about the surface of the sample.

27 Measurement of Topographic and Crystalline Information from a Sample

To measure topographic and crystalline information from a sample, thesample is fixed in position on a sample mount in a gas field ionmicroscope as described herein. The gas field ion microscope isconfigured as described in Example 19.

Crystalline information from the sample is measured as described inExample 21.

To measure topographic information from the sample, the total intensityof secondary electrons from the sample is measured as described inExample 25. The measured crystalline information is used to removecontributions to the secondary electron intensity measurements, at eachdetector, that arise from crystal structure variations in the sample.The corrected total secondary electron intensity values are used toconstruct grayscale images of the sample as described in Example 25.Information from the images measured by the multiple detectors can thenbe combined and used to determine quantitative three-dimensionaltopographic information about the surface of the sample.

28 Measurement of Topographic and Crystalline Information from a Sample

To measure topographic and crystalline information from a sample, thesample is fixed in position on a sample mount in a gas field ionmicroscope as described herein. The gas field ion microscope isconfigured as described in Example 19.

Crystalline information from the sample is measured as described inExample 19.

To measure topographic information from the sample, a detectorconfigured to measure He ions is positioned to detect He ions scatteredfrom the surface of the sample at large scattering angles. The He ionbeam is raster-scanned in discrete steps over the entire FOV region ofthe sample surface, and the total abundance of He ions is measured bythe detector as a function of the position of the He ion beam on thesample surface. The total abundance values are used to construct agrayscale image of the sample, where the gray level at a particularimage pixel is determined by the total measured abundance of scatteredHe ions at a corresponding He ion beam position on the sample.Topographic information is provided by the image, which shows thesurface relief pattern of the sample in the FOV.

29 Measurement of Topographic and Crystalline Information from a Sample

To measure topographic and crystalline information from a sample, thesample is fixed in position on a sample mount in a gas field ionmicroscope as described herein. The gas field ion microscope isconfigured as described in Example 19.

Crystalline information from the sample is measured as described inExample 20.

Topographic information from the sample is measured as described inExample 28.

30 Measurement of Topographic and Crystalline Information from a Sample

To measure topographic and crystalline information from a sample, thesample is fixed in position on a sample mount in a gas field ionmicroscope as described herein. The gas field ion microscope isconfigured as described in Example 19.

Crystalline information from the sample is measured as described inExample 31.

Topographic information from the sample is measured as described inExample 28.

31 Measurement of Topographic and Crystalline Information from a Sample

To measure topographic and crystalline information from a sample, thesample is fixed in position on a sample mount in a gas field ionmicroscope as described herein. The gas field ion microscope isconfigured as described in Example 19.

Crystalline information from the sample is measured as described inExample 19.

To measure topographic information from the sample, two or moredetectors configured to measure He ions are positioned to detect He ionsscattered from the surface of the sample at large scattering angles. TheHe ion beam is raster-scanned in discrete steps over the entire FOVregion of the sample surface, and the total abundance of He ions ismeasured by each of the detectors as a function of the position of theHe ion beam on the sample surface. The total abundance values are usedto construct grayscale images of the sample corresponding to each of thedetectors, where the gray level at a particular image pixel isdetermined by the total measured abundance of scattered He ions at acorresponding He ion beam position on the sample. Information from themultiple images measured by the detectors can then be combined and usedto determine quantitative three-dimensional topographic informationabout the surface of the sample.

32 Measurement of Topographic and Crystalline Information from a Sample

To measure topographic and crystalline information from a sample, thesample is fixed in position on a sample mount in a gas field ionmicroscope as described herein. The gas field ion microscope isconfigured as described in Example 19.

Crystalline information from the sample is measured as described inExample 20.

Topographic information from the sample is measured as described inExample 31.

33 Measurement of Topographic and Crystalline Information from a Sample

To measure topographic and crystalline information from a sample, thesample is fixed in position on a sample mount in a gas field ionmicroscope as described herein. The gas field ion microscope isconfigured as described in Example 19.

Crystalline information from the sample is measured as described inExample 21.

Topographic information from the sample is measured as described inExample 31.

34 Measurement of Topographic and Material Information from a Sample

To measure topographic and material information from a sample, thesample is fixed in position on a sample mount in a gas field ionmicroscope as described herein. The gas field ion microscope isconfigured as described in Example 19.

To measure material information from the sample, a detector configuredto measure He ions is positioned to detect He ions backscattered fromthe sample. The He ion beam is raster-scanned in discrete steps over theentire FOV region of the sample surface, and the total abundance ofbackscattered He ions is measured as a function of the position of theHe ion beam on the sample surface. The total abundance measurements ofbackscattered He ions are used to construct a grayscale image of thesample, where the gray level at a particular image pixel is determinedby the total measured abundance of backscattered He ions at acorresponding He ion beam position on the sample. Because the He ionscattering cross-sections depends roughly on the square of the atomicnumber of the scattering atom, the intensities in the image can be usedto quantitatively determine the composition of the sample.

To measure topographic information from the sample, a total intensity ofsecondary electrons is measured as a function of the position of the Heion beam on the sample surface as described in Example 19. The measuredmaterial information is then used to remove contributions to the totalsecondary electron intensity measurements that arise from compositionvariations in the sample. The corrected total secondary electronintensity values are used to construct a grayscale image of the sample,where the gray level at a particular image pixel is determined by thecorrected total intensity values. Topographic information is provided bythe image, which shows the surface relief pattern of the sample in theFOV.

35 Measurement of Topographic and Material Information from a Sample

To measure topographic and material information from a sample, thesample is fixed in position on a sample mount in a gas field ionmicroscope as described herein. The gas field ion microscope isconfigured as described in Example 19.

Material information can be measured from a sample as described inExample 34.

To measure topographic information from the sample, the total intensityof secondary electrons from the sample is measured as described inExample 22. The measured material information is used to removecontributions to the secondary electron intensity measurements, at eachion beam angle of incidence, that arise from composition variations inthe sample. The corrected total secondary electron intensity values areused to construct grayscale images of the sample as described in Example22. The information from the two images measured at different He ionbeam angles of incidence can then be combined and used to determinequantitative three-dimensional topographic information about the surfaceof the sample.

36 Measurement of Topographic and Material Information from a Sample

To measure topographic and material information from a sample, thesample is fixed in position on a sample mount in a gas field ionmicroscope as described herein. The gas field ion microscope isconfigured as described in Example 19.

Material information can be measured from a sample as described inExample 34.

To measure topographic information from the sample, the total intensityof secondary electrons from the sample is measured as described inExample 25. The measured material information is used to removecontributions to the secondary electron intensity measurements, at eachdetector, that arise from composition variations in the sample. Thecorrected total secondary electron intensity values are used toconstruct grayscale images of the sample as described in Example 25.Information from the images measured by the multiple detectors can thenbe combined and used to determine quantitative three-dimensionaltopographic information about the surface of the sample.

37 Measurement of Topographic and Material Information from a Sample

To measure topographic and material information from a sample, thesample is fixed in position on a sample mount in a gas field ionmicroscope as described herein. The gas field ion microscope isconfigured as described in Example 19.

Material information can be measured from the sample as described inExample 34.

Topographic information from the sample is measured as described inExample 28.

38 Measurement of Topographic and Material Information from a Sample

To measure topographic and material information from a sample, thesample is fixed in position on a sample mount in a gas field ionmicroscope as described herein. The gas field ion microscope isconfigured as described in Example 19.

Material information can be measured from the sample as described inExample 34.

Topographic information from the sample is measured as described inExample 31.

39 Measurement of Topographic and Material Information from a Sample

To measure topographic and material information from a sample, thesample is fixed in position on a sample mount in a gas field ionmicroscope as described herein. The gas field ion microscope isconfigured as described in Example 19.

To measure material information from the sample, a energy- andangle-resolved detector configured to measure He ions is positioned todetect He from the sample. The He ion beam is raster-scanned in discretesteps over the entire FOV region of the sample surface, and the energiesand angles of scattered He ions are measured as a function of theposition of the He ion beam on the sample surface. From the averageangles and energies of the scattered He ions, the mass of the scatteringatoms can be determined, and the composition of the sample can bedetermined.

To measure topographic information from the sample, a total intensity ofsecondary electrons is measured as a function of the position of the Heion beam on the sample surface as described in Example 19. The measuredmaterial information is then used to remove contributions to the totalsecondary electron intensity measurements that arise from compositionvariations in the sample. The corrected total secondary electronintensity values are used to construct a grayscale image of the sample,where the gray level at a particular image pixel is determined by thecorrected total intensity values. Topographic information is provided bythe image, which shows the surface relief pattern of the sample in theFOV.

40 Measurement of Topographic and Material Information from a Sample

To measure topographic and material information from a sample, thesample is fixed in position on a sample mount in a gas field ionmicroscope as described herein. The gas field ion microscope isconfigured as described in Example 19.

Material information can be measured from the sample as described inExample 39.

To measure topographic information from the sample, the total intensityof secondary electrons from the sample is measured as described inExample 22. The measured material information is used to removecontributions to the secondary electron intensity measurements, at eachion beam angle of incidence, that arise from composition variations inthe sample. The corrected total secondary electron intensity values areused to construct grayscale images of the sample as described in Example22. The information from the two images measured at different He ionbeam angles of incidence can then be combined and used to determinequantitative three-dimensional topographic information about the surfaceof the sample.

41 Measurement of Topographic and Material Information from a Sample

To measure topographic and material information from a sample, thesample is fixed in position on a sample mount in a gas field ionmicroscope as described herein. The gas field ion microscope isconfigured as described in Example 19.

Material information can be measured from the sample as described inExample 39.

To measure topographic information from the sample, the total intensityof secondary electrons from the sample is measured as described inExample 25. The measured material information is used to removecontributions to the secondary electron intensity measurements, at eachdetector, that arise from composition variations in the sample. Thecorrected total secondary electron intensity values are used toconstruct grayscale images of the sample as described in Example 25.Information from the images measured by the multiple detectors can thenbe combined and used to determine quantitative three-dimensionaltopographic information about the surface of the sample.

42 Measurement of Topographic and Material Information from a Sample

To measure topographic and material information from a sample, thesample is fixed in position on a sample mount in a gas field ionmicroscope as described herein. The gas field ion microscope isconfigured as described in Example 19.

Material information can be measured from the sample as described inExample 39.

Topographic information from the sample is measured as described inExample 28.

43 Measurement of Topographic and Material Information from a Sample

To measure topographic and material information from a sample, thesample is fixed in position on a sample mount in a gas field ionmicroscope as described herein. The gas field ion microscope isconfigured as described in Example 19.

Material information can be measured from the sample as described inExample 39.

Topographic information from the sample is measured as described inExample 31.

44 Measurement of Topographic and Material Information from a Sample

To measure topographic and material information from a sample, thesample is fixed in position on a sample mount in a gas field ionmicroscope as described herein. The gas field ion microscope isconfigured as described in Example 19.

To measure material information, an x-ray detector can be used to detectx-rays emerging from the sample in response to the incident He ion beam.The He ion beam is raster-scanned in discrete steps over the entire FOVregion of the sample surface, and the x-ray emission spectrum ismeasured as a function of the position of the He ion beam on the samplesurface. Certain emission lines in the x-ray spectrum are particular tocertain types of atoms, and so based on the measured x-ray spectrum, thecomposition at each step on the surface of the sample is determined.

To measure topographic information from the sample, a total intensity ofsecondary electrons is measured as a function of the position of the Heion beam on the sample surface as described in Example 19. The measuredmaterial information is then used to remove contributions to the totalsecondary electron intensity measurements that arise from compositionvariations in the sample. The corrected total secondary electronintensity values are used to construct a grayscale image of the sample,where the gray level at a particular image pixel is determined by thecorrected total intensity values. Topographic information is provided bythe image, which shows the surface relief pattern of the sample in theFOV.

45 Measurement of Topographic and Material Information from a Sample

To measure topographic and material information from a sample, thesample is fixed in position on a sample mount in a gas field ionmicroscope as described herein. The gas field ion microscope isconfigured as described in Example 19.

Material information can be measured from the sample as described inExample 44.

To measure topographic information from the sample, the total intensityof secondary electrons from the sample is measured as described inExample 22. The measured material information is used to removecontributions to the secondary electron intensity measurements, at eachion beam angle of incidence, that arise from composition variations inthe sample. The corrected total secondary electron intensity values areused to construct grayscale images of the sample as described in Example22. The information from the two images measured at different He ionbeam angles of incidence can then be combined and used to determinequantitative three-dimensional topographic information about the surfaceof the sample.

46 Measurement of Topographic and Material Information from a Sample

To measure topographic and material information from a sample, thesample is fixed in position on a sample mount in a gas field ionmicroscope as described herein. The gas field ion microscope isconfigured as described in Example 19.

Material information can be measured from the sample as described inExample 44.

To measure topographic information from the sample, the total intensityof secondary electrons from the sample is measured as described inExample 25. The measured material information is used to removecontributions to the secondary electron intensity measurements, at eachdetector, that arise from composition variations in the sample. Thecorrected total secondary electron intensity values are used toconstruct grayscale images of the sample as described in Example 25.Information from the images measured by the multiple detectors can thenbe combined and used to determine quantitative three-dimensionaltopographic information about the surface of the sample.

47 Measurement of Topographic and Material Information from a Sample

To measure topographic and material information from a sample, thesample is fixed in position on a sample mount in a gas field ionmicroscope as described herein. The gas field ion microscope isconfigured as described in Example 19.

Material information can be measured from the sample as described inExample 44.

Topographic information from the sample is measured as described inExample 28.

48 Measurement of Topographic and Material Information from a Sample

To measure topographic and material information from a sample, thesample is fixed in position on a sample mount in a gas field ionmicroscope as described herein. The gas field ion microscope isconfigured as described in Example 19.

Material information can be measured from the sample as described inExample 44.

Topographic information from the sample is measured as described inExample 31.

49 Measurement of Topographic and Material Information from a Sample

To measure topographic and material information from a sample, thesample is fixed in position on a sample mount in a gas field ionmicroscope as described herein. The gas field ion microscope isconfigured as described in Example 19.

To measure material information, a photon detector can be used to detectphotons emerging from the sample in response to the incident He ionbeam. The He ion beam is raster-scanned in discrete steps over theentire FOV region of the sample surface, and the photon emissionspectrum is measured as a function of the position of the He ion beam onthe sample surface. Certain emission lines in the spectrum areparticular to certain types of atoms, and so based on the measuredspectrum, the composition at each step on the surface of the sample isdetermined.

To measure topographic information from the sample, a total intensity ofsecondary electrons is measured as a function of the position of the Heion beam on the sample surface as described in Example 19. The measuredmaterial information is then used to remove contributions to the totalsecondary electron intensity measurements that arise from compositionvariations in the sample. The corrected total secondary electronintensity values are used to construct a grayscale image of the sample,where the gray level at a particular image pixel is determined by thecorrected total intensity values. Topographic information is provided bythe image, which shows the surface relief pattern of the sample in theFOV.

50 Measurement of Topographic and Material Information from a Sample

To measure topographic and material information from a sample, thesample is fixed in position on a sample mount in a gas field ionmicroscope as described herein. The gas field ion microscope isconfigured as described in Example 19.

Material information can be measured from the sample as described inExample 49.

To measure topographic information from the sample, the total intensityof secondary electrons from the sample is measured as described inExample 22. The measured material information is used to removecontributions to the secondary electron intensity measurements, at eachion beam angle of incidence, that arise from composition variations inthe sample. The corrected total secondary electron intensity values areused to construct grayscale images of the sample as described in Example22. The information from the two images measured at different He ionbeam angles of incidence can then be combined and used to determinequantitative three-dimensional topographic information about the surfaceof the sample.

51 Measurement of Topographic and Material Information from a Sample

To measure topographic and material information from a sample, thesample is fixed in position on a sample mount in a gas field ionmicroscope as described herein. The gas field ion microscope isconfigured as described in Example 19.

Material information can be measured from the sample as described inExample 49.

To measure topographic information from the sample, the total intensityof secondary electrons from the sample is measured as described inExample 25. The measured material information is used to removecontributions to the secondary electron intensity measurements, at eachdetector, that arise from composition variations in the sample. Thecorrected total secondary electron intensity values are used toconstruct grayscale images of the sample as described in Example 25.Information from the images measured by the multiple detectors can thenbe combined and used to determine quantitative three-dimensionaltopographic information about the surface of the sample.

52 Measurement of Topographic and Material Information from a Sample

To measure topographic and material information from a sample, thesample is fixed in position on a sample mount in a gas field ionmicroscope as described herein. The gas field ion microscope isconfigured as described in Example 19.

Material information can be measured from the sample as described inExample 49.

Topographic information from the sample is measured as described inExample 28.

53 Measurement of Topographic and Material Information from a Sample

To measure topographic and material information from a sample, thesample is fixed in position on a sample mount in a gas field ionmicroscope as described herein. The gas field ion microscope isconfigured as described in Example 19.

Material information can be measured from the sample as described inExample 49.

Topographic information from the sample is measured as described inExample 31.

54 Measurement of Topographic and Material Information from a Sample

To measure topographic and material information from a sample, thesample is fixed in position on a sample mount in a gas field ionmicroscope as described herein. The gas field ion microscope isconfigured as described in Example 19.

To measure material information, an Auger electron detector can be usedto detect Auger electrons emerging from the sample in response to theincident He ion beam. The He ion beam is raster-scanned in discretesteps over the entire FOV region of the sample surface, and the Augerelectron emission spectrum is measured as a function of the position ofthe He ion beam on the sample surface. Certain emission lines in thespectrum are particular to certain types of atoms, and so based on themeasured spectrum, the composition at each step on the surface of thesample is determined.

To measure topographic information from the sample, a total intensity ofsecondary electrons is measured as a function of the position of the Heion beam on the sample surface as described in Example 19. The measuredmaterial information is then used to remove contributions to the totalsecondary electron intensity measurements that arise from compositionvariations in the sample. The corrected total secondary electronintensity values are used to construct a grayscale image of the sample,where the gray level at a particular image pixel is determined by thecorrected total intensity values. Topographic information is provided bythe image, which shows the surface relief pattern of the sample in theFOV.

55 Measurement of Topographic and Material Information from a Sample

To measure topographic and material information from a sample, thesample is fixed in position on a sample mount in a gas field ionmicroscope as described herein. The gas field ion microscope isconfigured as described in Example 19.

Material information can be measured from the sample as described inExample 54.

To measure topographic information from the sample, the total intensityof secondary electrons from the sample is measured as described inExample 22. The measured material information is used to removecontributions to the secondary electron intensity measurements, at eachion beam angle of incidence, that arise from composition variations inthe sample. The corrected total secondary electron intensity values areused to construct grayscale images of the sample as described in Example22. The information from the two images measured at different He ionbeam angles of incidence can then be combined and used to determinequantitative three-dimensional topographic information about the surfaceof the sample.

56 Measurement of Topographic and Material Information from a Sample

To measure topographic and material information from a sample, thesample is fixed in position on a sample mount in a gas field ionmicroscope as described herein. The gas field ion microscope isconfigured as described in Example 19.

Material information can be measured from the sample as described inExample 54.

To measure topographic information from the sample, the total intensityof secondary electrons from the sample is measured as described inExample 25. The measured material information is used to removecontributions to the secondary electron intensity measurements, at eachdetector, that arise from composition variations in the sample. Thecorrected total secondary electron intensity values are used toconstruct grayscale images of the sample as described in Example 25.Information from the images measured by the multiple detectors can thenbe combined and used to determine quantitative three-dimensionaltopographic information about the surface of the sample.

57 Measurement of Topographic and Material Information from a Sample

To measure topographic and material information from a sample, thesample is fixed in position on a sample mount in a gas field ionmicroscope as described herein. The gas field ion microscope isconfigured as described in Example 19.

Material information can be measured from the sample as described inExample 54.

Topographic information from the sample is measured as described inExample 28.

58 Measurement of Topographic and Material Information from a Sample

To measure topographic and material information from a sample, thesample is fixed in position on a sample mount in a gas field ionmicroscope as described herein. The gas field ion microscope isconfigured as described in Example 19.

Material information can be measured from the sample as described inExample 54.

Topographic information from the sample is measured as described inExample 31.

59 Measurement of Topographic and Material Information from a Sample

To measure topographic and material information from a sample, thesample is fixed in position on a sample mount in a gas field ionmicroscope as described herein. The gas field ion microscope isconfigured as described in Example 19.

To measure material information, a TOF detector can be used to detectsecondary ions and/or atoms emerging from the sample in response to theincident He ion beam. The He ion beam is raster-scanned in discretesteps over the entire FOV region of the sample surface, and thetimes-of-flight of secondary ions and/or atoms from sample 180 aremeasured as a function of the position of the He ion beam on the samplesurface. Based on the measured times-of-flight of the ions/atoms, andthe known voltage of the accelerating electrodes in the TOF instrument,the masses of the detected particles can be calculated and theidentities of the particles can be determined.

To measure topographic information from the sample, a total intensity ofsecondary electrons is measured as a function of the position of the Heion beam on the sample surface as described in Example 19. The measuredmaterial information is then used to remove contributions to the totalsecondary electron intensity measurements that arise from compositionvariations in the sample. The corrected total secondary electronintensity values are used to construct a grayscale image of the sample,where the gray level at a particular image pixel is determined by thecorrected total intensity values. Topographic information is provided bythe image, which shows the surface relief pattern of the sample in theFOV.

60 Measurement of Topographic and Material Information from a Sample

To measure topographic and material information from a sample, thesample is fixed in position on a sample mount in a gas field ionmicroscope as described herein. The gas field ion microscope isconfigured as described in Example 19

Material information can be measured from the sample as described inExample 59

To measure topographic information from the sample, the total intensityof secondary electrons from the sample is measured as described inExample 22. The measured material information is used to removecontributions to the secondary electron intensity measurements, at eachion beam angle of incidence, that arise from composition variations inthe sample. The corrected total secondary electron intensity values areused to construct grayscale images of the sample as described in 22. Theinformation from the two images measured at different He ion beam anglesof incidence can then be combined and used to determine quantitativethree-dimensional topographic information about the surface of thesample.

61 Measurement of Topographic and Material Information from a Sample

To measure topographic and material information from a sample, thesample is fixed in position on a sample mount in a gas field ionmicroscope as described herein. The gas field ion microscope isconfigured as described in Example 19.

Material information can be measured from the sample as described inExample 59.

To measure topographic information from the sample, the total intensityof secondary electrons from the sample is measured as described inExample 25. The measured material information is used to removecontributions to the secondary electron intensity measurements, at eachdetector, that arise from composition variations in the sample. Thecorrected total secondary electron intensity values are used toconstruct grayscale images of the sample as described in Example 25.Information from the images measured by the multiple detectors can thenbe combined and used to determine quantitative three-dimensionaltopographic information about the surface of the sample.

62 Measurement of Topographic and Material Information from a Sample

To measure topographic and material information from a sample, thesample is fixed in position on a sample mount in a gas field ionmicroscope as described herein. The gas field ion microscope isconfigured as described in Example 19.

Material information can be measured from the sample as described inExample 59.

Topographic information from the sample is measured as described inExample 28.

63 Measurement of Topographic and Material Information from a Sample

To measure topographic and material information from a sample, thesample is fixed in position on a sample mount in a gas field ionmicroscope as described herein. The gas field ion microscope isconfigured as described in Example 19.

Material information can be measured from the sample as described inExample 59.

Topographic information from the sample is measured as described inExample 31.

64 Measurement of Crystalline and Material Information from a Sample

To measure topographic and material information from a sample, thesample is fixed in position on a sample mount in a gas field ionmicroscope as described herein. The gas field ion microscope isconfigured as described in Example 192.

Material information can be measured from the sample as described inExample 44.

Crystalline information can be measured from the sample as described inExample 19.

65 Measurement of Crystalline and Material Information from a Sample

To measure topographic and material information from a sample, thesample is fixed in position on a sample mount in a gas field ionmicroscope as described herein. The gas field ion microscope isconfigured as described in Example 19.

Material information can be measured from the sample as described inExample 44.

Crystalline information can be measured from the sample as described inExample 20.

66 Measurement of Crystalline and Material Information from a Sample

To measure topographic and material information from a sample, thesample is fixed in position on a sample mount in a gas field ionmicroscope as described herein. The gas field ion microscope isconfigured as described in Example 19.

Material information can be measured from the sample as described inExample 44.

Crystalline information can be measured from the sample as described inExample 21.

67 Measurement of Crystalline and Material Information from a Sample

To measure topographic and material information from a sample, thesample is fixed in position on a sample mount in a gas field ionmicroscope as described herein. The gas field ion microscope isconfigured as described in Example 19.

Material information can be measured from the sample as described inExample 49.

Crystalline information can be measured from the sample as described inExample 19.

68 Measurement of Crystalline and Material Information from a Sample

To measure topographic and material information from a sample, thesample is fixed in position on a sample mount in a gas field ionmicroscope as described herein. The gas field ion microscope isconfigured as described in Example 19.

Material information can be measured from the sample as described inExample 49.

Crystalline information can be measured from the sample as described inExample 20.

69 Measurement of Crystalline and Material Information from a Sample

To measure topographic and material information from a sample, thesample is fixed in position on a sample mount in a gas field ionmicroscope as described herein. The gas field ion microscope isconfigured as described in Example 19.

Material information can be measured from the sample as described inExample 49.

Crystalline information can be measured from the sample as described inExample 214.

70 Measurement of Crystalline and Material Information from a Sample

To measure topographic and material information from a sample, thesample is fixed in position on a sample mount in a gas field ionmicroscope as described herein. The gas field ion microscope isconfigured as described in Example 19.

Material information can be measured from the sample as described inExample 54.

Crystalline information can be measured from the sample as described inExample 19.

71 Measurement of Crystalline and Material Information from a Sample

To measure topographic and material information from a sample, thesample is fixed in position on a sample mount in a gas field ionmicroscope as described herein. The gas field ion microscope isconfigured as described in Example 19.

Material information can be measured from the sample as described inExample 54.

Crystalline information can be measured from the sample as described inExample 20.

72 Measurement of Crystalline and Material Information from a Sample

To measure topographic and material information from a sample, thesample is fixed in position on a sample mount in a gas field ionmicroscope as described herein. The gas field ion microscope isconfigured as described in Example 19.

Material information can be measured from the sample as described inExample 54.

Crystalline information can be measured from the sample as described inExample 21.

73 Measurement of Crystalline and Material Information from a Sample

To measure topographic and material information from a sample, thesample is fixed in position on a sample mount in a gas field ionmicroscope as described herein. The gas field ion microscope isconfigured as described in Example 19.

Material information can be measured from the sample as described inExample 59.

Crystalline information can be measured from the sample as described inExample 192.

74 Measurement of Crystalline and Material Information from a Sample

To measure topographic and material information from a sample, thesample is fixed in position on a sample mount in a gas field ionmicroscope as described herein. The gas field ion microscope isconfigured as described in Example 19.

Material information can be measured from the sample as described inExample 59.

Crystalline information can be measured from the sample as described inExample 20.

75 Measurement of Crystalline and Material Information from a Sample

To measure topographic and material information from a sample, thesample is fixed in position on a sample mount in a gas field ionmicroscope as described herein. The gas field ion microscope isconfigured as described in Example 19.

Material information can be measured from the sample as described inExample 59.

Crystalline information can be measured from the sample as described inExample 21.

Other embodiments are in the claims.

1. A system, comprising: a gas field ion source having an electricallyconductive tip with a terminal shelf comprising one or more atoms,wherein the system is configured so that, during use of the system, theone or more atoms interact with a gas to generate an ion beam, and 70%or more of the ions in the ion beam that reach a surface of a sample aregenerated via an interaction of the gas with only one atom of the one ormore atoms.
 2. The system of claim 1, wherein, during use, 75% or moreof the ions in the ion beam that reach a surface of a sample aregenerated via an interaction of the gas with only one atom of the one ormore atoms.
 3. The system of claim 1, wherein, during use, 80% or moreof the ions in the ion beam that reach a surface of a sample aregenerated via an interaction of the gas with only one atom of the one ormore atoms.
 4. The system of claim 1, wherein, during use, 85% or moreof the ions of the ions in the ion beam that reach a surface of a sampleare generated via an interaction of the gas with only one atom of theone or more atoms.
 5. The system of claim 1, further comprising ionoptics that include electrodes and an aperture.
 6. The system of claim5, wherein the aperture is a disk.
 7. The system of claim 5, wherein theaperture has multiple openings.
 8. The system of claim 1, wherein theterminal shelf comprises 20 atoms or less.
 9. The system of claim 1,wherein the terminal shelf is a trimer.
 10. The system of claim 1,wherein the electrically conductive tip has an average radius ofcurvature of 200 nm or less.
 11. The system of claim 1, wherein theelectrically conductive tip has an average full cone angle of from 15°to 45°.
 12. The system of claim 1, the electrically conductive tip hasaverage cone direction of 10° or less.
 13. The system of claim 1,wherein the electrically conductive tip includes an end that comprises asingle crystal that is aligned with a longitudinal axis of theelectrically conductive to within 3° or less.
 14. The system of claim 1,wherein the electrically conductive tip comprises a material selectedfrom the group consisting of tungsten, carbon, tantalum, iridium,rhenium, niobium, platinum and molybdenum.
 15. The system of claim 1,wherein the electrically conductive tip is a tungsten tip.
 16. Thesystem of claim 1, wherein the electrically conductive tip is a W(111)tip.
 17. The system of claim 16, wherein the terminal shelf is a trimer.18. The system of claim 1, wherein the system is a gas field ionmicroscope.
 19. The system of claim 1, wherein the system is a heliumion microscope.
 20. The system of claim 1, wherein the system is ascanning ion microscope.
 21. The system of claim 1, wherein the systemis a scanning helium ion microscope.
 22. The system of claim 1, furthercomprising a mechanism, the gas field ion source including anelectrically conductive tip, the mechanism being coupled to the gasfield ion source so that the mechanism can translate the electricallyconductive tip, tilt the electrically conductive tip or both.
 23. Thesystem of claim 22, wherein the mechanism comprises a curved surface.24. The system of claim 22, wherein the mechanism tilts the ion sourcerelative to the aperture.
 25. The system of claim 22, wherein theelectrically conductive tip is a W(111) tip, and the terminal shelf is atrimer.
 26. The system of claim 1, wherein the system is a gas field ionmicroscope having a damage test value is 25 nm or less.
 27. The systemof claim 1, wherein the system is a gas field ion microscope having aquality factor of 0.25 or more.
 28. The system of claim 1, wherein thesystem is a gas field ion microscope that is capable of producing animage of a sample, the image of the sample having a resolution of 10 nmor less.
 29. The system of claim 1, wherein the gas field ion source iscapable of interacting with the gas to generate an ion beam for a timeperiod of one week or more with a maximum interruption time of 10 hoursor less.
 30. The system of claim 1, wherein gas field ion sourcecomprises an electrically conductive tip, the ion source being capableof interacting with the gas to generate the ion beam for a time periodof one week or more without removing the electrically conductive tipfrom the system.
 31. The system of claim 1, wherein the ion beam has areduced etendue of 1×10⁻¹⁶ cm²srV or less.
 32. The system of claim 1,wherein the ion beam has an etendue of 5×10⁻²¹ cm²sr or less.
 33. Thesystem of claim 1, wherein the ion beam has a reduced brightness at thesurface of the sample of 5×10⁸ A/m²srV or more.
 34. The system of claim1, wherein the ion beam has a brightness at the surface of the sample of1×10⁹ A/cm²sr or more.
 35. The system of claim 1, wherein the ion beamhas a spot size with a dimension of 10 nm or less at the surface of thesample.
 36. The system of claim 1, wherein the ion beam has an ion beamcurrent at the surface of the sample of one nA or less.
 37. The systemof claim 36, wherein the ion beam current at the surface of the sampleis 0.1 fA or more.
 38. The system of claim 1, wherein the ion beam hasan energy spread at the surface of the sample of five eV or less. 39.The system of claim 1, further comprising the sample, wherein the gasfield ion source including a tip, and the surface of the sample is fivecm or more from the tip.
 40. The system of claim 1, further comprising acoolant source thermally coupled to the gas field ion source so thatduring operation of the ion source the temperature of the ion source is5 K or more.
 41. The system of claim 1, further comprising a cryogenicrefrigerator source thermally coupled to the gas field ion source sothat during operation of the ion source the temperature of the ionsource is 5 K or more.
 42. The system of claim 1, wherein the ion beamhaving a convergence half angle of 5 mrad or less at a surface of thesample.
 43. The system of claim 1, wherein the gas field ion sourcecomprises an electrically conductive tip having a terminal shelf with 20atoms or less.
 44. A system, comprising: a gas field ion sourceincluding an electrically conductive tip capable of interacting with agas to generate an ion beam; ion optics configured so that during use atleast a portion of the ion beam passes through the ion optics; and amoving mechanism coupled to the gas field ion source so that the movingmechanism can translate the electrically conductive tip, tilt theelectrically conductive tip or both. 45-87. (canceled)
 88. A system,comprising: a gas field ion source including an electrically conductivetip with an average full cone angle of from 15° to 45°. 89-104.(canceled)
 105. A system, comprising: a gas field ion source includingan electrically conductive tip with an average radius of curvature of200 nm or less. 106-121. (canceled)